Cordless telephones are one of those minor miracles of modern life -- with a cordless phone, you can talk on the phone while moving freely about your house or in your yard. Long before cell phones became so cheap that anyone could afford one, cordless phones gave everyone cell phone freedom within the privacy of their own homes. With some features, you can now have three-way conversations, page someone within your house or work with your hands while you talk on the phone.

Cordless phones have many of the same features as standard telephones and there are many models available. In this edition of How Stuff Works, we will examine how these cordless telephones work and why there are so many different types on the market today!

To access all of the different parts of this article, choose from the map below:

You may want to start with "How They Work" to learn the basics about cordless phones. If you are thinking about buying one, be sure to look at the Features section to learn about all of the features you should keep in mind to buy the right cordless phone for you.

The Basics
A cordless telephone is basically a combination telephone and radio transmitter/receiver (see How Telephones Work and How Radio Works for details on these two technologies). A cordless phone has two major parts: base and handset.

• The base is attached to the phone jack through a standard phone wire connection, and as far as the phone system is concerned it looks just like a normal phone. The base receives the incoming call (as an electrical signal) through the phone line, converts it to an FM radio signal and then broadcasts that signal.

• The handset receives the radio signal from the base, converts it to an electrical signal and sends that signal to the speaker, where it is converted into the sound you hear. When you talk, the handset broadcasts your voice through a second FM radio signal back to the base. The base receives your voice signal, converts it to an electrical signal and sends that signal through the phone line to the other party.

Diagram showing how the base unit and handset of the cordless phone talk to each other. Each color represents a different frequency.

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A Brief History of Cordless Telephones
Cordless phones first appeared around 1980. The earliest cordless phones operated at a frequency of 27 MHz. They had the following problems:

• limited range
• poor sound quality - noisy and ridden with static because walls and appliances interfered with the signals
• poor security - people could easily intercept signals from another cordless phone because of the limited number of channels

Because the 43-50 MHz cordless phone frequency was becoming increasingly crowded, the FCC granted the frequency range of 900 MHz in 1990. This higher frequency allowed cordless phones to be clearer, broadcast a longer distance and choose from more channels. However, cordless phones were still quite expensive, about $400.

In 1994, digital cordless phones in the 900 MHz frequency range were introduced. Digital signals allowed the phones to be more secure and decreased eavesdropping -- it was pretty easy to eavesdrop on analog cordless phone conversations. In 1995, digital spread spectrum (DSS) was introduced for cordless phones. This technology enabled the digital information to spread in pieces over several frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on the cordless conversations.

In 1998, the FCC opened up the 2.4 GHz range for cordless phone use. This frequency has increased the distance over which a cordless phone can operate, and brought it out of the frequency range of most radio scanners, thereby further increasing security.

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Anatomy of a Cordless Telephone
To illustrate the parts of a cordless telephone, we will show you the inside of this one from General Electric (GE). It was made in 1993 and operated in the 43-50 MHz range.

GE cordless phone, including handset and base unit

As mentioned above, all cordless phones have a base and a handset. Let's look at these parts individually.

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Base
The base unit of the cordless phone is plugged into the telephone jack on your wall.

Base unit components

If you open up the base and expose the circuit board, you see several components that carry out the functions of the base:

• phone line interface - receives and sends telephone signals through the phone line
• radio
  • amplifies signals to and from phone-line interface, user controls and speaker phone (if present)
  • broadcasts and receives radio signals to and from the handset
• power - supplies low voltage power to the circuits and recharges the battery of the handset

Circuit board in the base of the GE cordless phone

Phone Line Interface
Phone line interface components do two things. First, they send the ringer signal to the bell (if it's on the base) or to the radio components for broadcast to the handset. This lets you know that you have an incoming call. Second, they receive and send small changes in the phone line's electrical current to and from the radio components of the base. When you talk, you cause small changes in the electrical current of the phone line, and these changes get sent to your caller. The same happens when the caller talks to you.

Radio Components
The radio components receive the electrical signals from the phone line interface and user controls (keypads, buttons). The radio components convert the signals to radio waves and broadcast them via the antenna. Radio components use quartz crystals to set the radio frequencies for sending and receiving. There are two quartz crystals, one for sending signals and one for receiving signals. Remember that the base and handset operate on a frequency pair that allows you to talk and listen at the same time (duplex). The radio components include an audio amplifier that increases the strength of the incoming electrical signals.

Power Components
A DC power cube transformer supplies the low voltage required by the electrical components on the circuit board. The power components on the circuit board work with the power cube to supply electrical current to re-charge the battery of the handset.

In addition to the above components, some bases also have audio amplifiers to drive speakers for speaker phone features, keypads for dialing, liquid crystal displays (LCD) for caller ID, light-emitting diodes (LED) for power/charging indicators, and solid state memory for answering machine or call-back features.

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Handset
You can carry the handset with you throughout the house or outside within the range of the base transmitter. The handset has all of the equipment of a standard telephone (speaker, microphone, dialing keypad), plus the equipment of an FM radio transmitter/receiver.

Block diagram of handset components

When you open up the handset, you see these components:

• speaker - converts electrical signals into the sound that you hear
• microphone - picks up your voice and changes it to electrical signals
• keypad - input for dialing
• buzzer or ringer - lets you know that you have an incoming call
• radio components
  • amplify electrical signals to and from microphone and speakers
  • send and receive FM radio frequencies
• LCD or LED displays - indicator lights
• re-chargeable battery - supplies electrical power to handset

Parts of the GE cordless phone's handset, showing the fronts of the circuit boards

Parts of the GE cordless phone's handset, showing the backs of the circuit boards, the speaker, microphone, ringer and battery

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Handset Components

Speaker
The speaker receives the electrical signals from the audio amplifier in the radio components and converts them into sound. When you remove the cover from the speaker, you see a large round permanent magnet with a hole in the middle and a deep groove surrounding the hole. Within this deep groove is a coil of fine copper wire that is attached to a thin plastic membrane. The plastic membrane covers the magnet and coil.

Close-up view of the speaker in the GE cordless telephone handset

Close-up of the speaker with the top removed

Close-up of the speaker with the plastic membrane and attached coil lifted out. The large metal disc is the magnet.

Close-up of the speaker's plastic membrane with attached wire coil

To hear sounds, the following events happen:

1. Electrical signals come from the radio components.
2. The electrical signals travel in the coil of copper wire.
3. The electrical signals induce magnetic currents in the coil of wire, thereby making it an electromagnet.
4. The electromagnetic coil moves in and out of the groove within the permanent magnet.
5. The coil moves the attached plastic membrane in and out at the same frequencies as the changes in electric currents.
6. The movements of the membrane move air at the same frequencies, thereby creating sound waves that you can hear.

Microphone
The microphone changes the sound waves from your voice into electrical signals that are sent to the audio amplifier of the radio components. A microphone is essentially a speaker that works in reverse. When sound waves from your voice move the membrane, they make tiny electric currents either by moving a coil of wire within a magnet or by compressing the membrane against carbon dust (see question 309 for details).

Close-up of handset's keypad circuit board with attached microphone and buzzer

Keypad
The keypad allows you to dial a number. It transfers the pressure from your fingertip on the appropriate key into an electrical signal that it sends to the radio components. Below the rubber keypad is a circuit board with black conductive material under each button (shown above). The keypad works like a remote control. When you press a button, it makes a contact with the black material and changes its electrical conductance. The conductance sends an electrical signal to the radio components indicating that you have selected that number.

Buzzer or Ringer
When the radio components of the handset receive the ringer signal from the base, they send electrical signals to the buzzer. The buzzer changes those electrical signals into sound much like the speaker does. You hear the buzzer sound and know that someone is calling you. In some phones, the speaker is used to make the ringer sound and there is no need for a separate ringer.

Radio Components

Duplex Example Base: 44.32 MHz transmitter 49.28 MHz receiver Handset: 49.28 MHz transmitter 44.32 MHz receiver

The radio components of the handset are like those of the base -- they convert electrical signals from the microphone into FM radio signals and broadcast them at the same frequency as the receiving crystal of the base unit. The radio components also receive radio signals at the same frequency as the broadcasting crystal from the base, convert them to electrical signals and send them to the speaker and/or buzzer (ringer).

Remember that the base and handset operate on a duplex frequency pair that allows you to talk and listen at the same time.

LCD or LED Displays
Most handsets have one or more light-emitting diodes (LED) that indicate various things, such as when the phone has an open line or when the battery is low.

LED indicator light on the handset of the GE cordless phone

Some handsets have an LCD that can display numbers for caller ID features, similar to a cell phone. The LCD may be reflective or backlit so that you can see it when the room light is low.

Battery
The handset's battery supplies the power for all of the electrical components in the handset. All cordless phone handsets have a rechargeable battery (nickel-cadmium, nickel-metal hydride or lithium). When the battery runs low, an indicator light on the handset usually lights up or flashes. In some phones, a "beeping" sound may also indicate a low battery. You then recharge the battery on the base of the cordless phone.

The GE cordless phone that we dissected was from 1993. Modern cordless phones have the same functions and much of the same hardware. However, many of the electronic circuits that were once achieved with transistors, resistors and capacitors have been replaced with integrated circuits. This advancement allows the handset to be either smaller with the same functions or the same size with more functions.

In summary, a cordless phone is basically a combination of a telephone and an FM radio transmitter/receiver. Because it is a radio transmitter, it broadcasts signals over the open airways rather than specifically between the base and handset.

Many cordless phone conversations can be easily picked up by radio scanners.

Because of this open broadcast, It is possible for other people to listen to your phone conversation by using a radio scanner. So an important issue and feature to look for in a cordless phone is security -- DSS offers the best protection against eavesdropping.

To go on to the "Features" section click here, or choose from the map below:

Features
Cordless phones have many of the same features as standard telephones, and there are many models, offering lots of different features. In this section of How Cordless Phones Work, we will examine the various features on these portable telephones.

When you think about cordless phone features, consider the following categories:

• major features of the phone - range, sound quality, security
• convenience features of the phone - ease of use
• options in combination with the phone service - making the most of your phone

To learn about features click here, or choose from the map below:

Major Features
Remember that a cordless telephone is a combination of a telephone and a radio transmitter/receiver (see How a Cordless Telephone Works for details). Because it is a radio transmitter/receiver, you have the following issues that you do not have on a standard cord phone:

• range
• sound quality
• security

The above issues relate to the following features of your cordless phone:

• radio frequency
• analog vs. digital technology
• number of channels

Frequency
Because your cordless phone is a radio transmitter/receiver, it operates on various radio frequencies, which are set by the Federal Communications Commission (FCC) as with any other radio. Cordless phones operate over three major frequency bands (base and receiver use two closely related but separate frequencies within the band so that you can talk and listen at the same time):

• 43-50 MHz
• 900 MHz
• 2.4 GHz

The 43-50 MHz band was common to early cordless telephones and is still available in low-cost models. Because of the low frequency, these phones have short ranges (about 1,000 ft / 330 m) and poorer sound quality (due to interference from structures and appliances). The 43-50 MHz phone signals can also be picked up easily on radio scanners and nearby baby monitors.

The 900 MHz band (actually 900-928 MHz) is the most common frequency for cordless phones today. The higher frequency gives it a greater range (5,000 to 7,000 ft / 1,500 to 2,100 m) and better sound quality. However, 900 MHz signals can be picked up easily by most commercially available radio scanners.

In 1998, the FCC opened up the 2.4 GHz range for cordless phone use. A 2.4 GHz cordless phone can operate over a greater distance and is above the frequencies that can be picked up by most commercially available radio scanners; therefore, it is more secure than lower frequency models. A 2.4 GHz cordless phone will be more expensive than a lower frequency phone.

Analog vs. Digital
Analog technology is common in cordless telephones, especially in inexpensive models. Analog signals tend to be more noisy, or prone to interference with respect to sound quality. In addition, analog signals are easily picked up and interpreted by radio scanners.

In contrast, digital technology, like that found in a CD, allows the phone signals to sound clearer. Furthermore, digital signals are more secure. In 1995, digital spread spectrum (DSS) was introduced for cordless phones. DSS spread the digital information in pieces over several frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on cordless phone conversations.

Channels
Each frequency band (43-50 MHz, 900 MHz or 2.4 GHz) can be subdivided into different increments or channels. For example, on some models, when you're talking on your 900 MHz phone, the base searches for a pair of frequencies (channels) within that range, that is not already in use, in order to talk to the handset. So, if the base is capable of searching more increments, it can more easily find a frequency pair that is clear from interference, providing better sound quality. The number of cordless phone channels can vary as follows:

• 10 to 25 channels - 43-50 MHz phones, some inexpensive 900 MHz phones
• 20 to 60 channels - most 900 MHz phones
• 50 to 100 channels - high-end 900 MHz and 2.4 GHz phones

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Convenience Features
Convenience features make the cordless phone easier to use or more versatile; some of these features are identical to those in standard cord phones. Convenience features include the following:

• speaker phones
• pager/handset locator
• indicators
  • low battery
  • out of range
• redial
• one-touch dialing/programmable
• volume control
• mute/hold
• ringer in base
• keypad on base
• battery
• extra battery charger
• hands-free headset
• wall mount

Speaker Phones
Speaker phones can be on the base and/or handset. Speaker phones have a microphone that can pick up the sounds around them and a speaker to broadcast incoming sounds. With a speaker phone, more than one person can talk and listen to the call at the same time. You can use a speaker phone for conferences or family conversations.

Pager/Handset Locator
With this feature, a button can be pressed on either the handset or the base to find whichever part you're missing. The button sends a radio signal to the other unit, and when the other unit receives the radio signal it sets off a beeper. This feature is most helpful in locating the handset. For example, my 19 month old son frequently runs off with our cordless handset and hides it somewhere. This feature makes it easy to find the handset. In addition, this feature can be used to page someone, or as an intercom. When I am upstairs and my wife is downstairs, we can use this feature to ask each other questions over the phone without having to yell up or down the staircase, because my base unit has a speaker phone.

Indicators
Indicators on the handset can be combinations of beeping sounds, LCD messages and flashing LED lights that tell you when your battery is low and needs to be recharged or when you are getting out of range of the phone's base unit. On the base unit, the indicators can tell you when the handset is done charging or off the hook.

Redial
With this feature, the handset or base unit has a memory chip that can store the last number called by the phone. To redial the number, you just touch the button on the handset and/or base and it dials that number through the phone line.

One-Touch Dialing/Programmable
Like with the redial feature, the handset or base unit has a memory chip that is capable of storing several numbers, usually 13 to 18. Each number can be activated at the touch of a key. This feature is convenient when you cannot remember a number, are outside or away from a phone book or need to dial an emergency number in a hurry.

Volume Control
This feature adjusts the sensitivity of the speaker, ringer and/or microphone so that you can hear and be heard by the caller. It is especially useful for conference calls on speaker phones.

Mute/Hold
With this feature, a switch temporarily disconnects the microphone of the handset and/or base unit. You can talk to someone else nearby without your caller hearing your conversation.

Ringer in Base
With this feature, you can tell when you have an incoming call even if the handset is not nearby.

Keypad in Base
This feature allows you to dial from the base to make a call even if you do not have the handset nearby. It is almost always found in combination with a speaker phone on the base. This feature keeps the phone usable when you have temporarily lost the handset (or your child has hidden it somewhere).

Photo of a cordless phone base unit with keypad and speaker phone

Battery
The handset's battery supplies the power for all of the electrical components in the handset. All cordless phone handsets have a rechargeable battery (nickel-cadmium, nickel-metal hydride or lithium). When the battery runs low, an indicator light on the handset usually lights up or flashes. In some phones, a "beeping " sound may also indicate a low battery. You then recharge the battery on the base of the cordless phone. Nickel-cadmium batteries are subject to a memory effect, so it is best to let them drain entirely before recharging them on the base; nickel-metal hydride and lithium batteries have no memory effect.

Extra Battery Charger
Some cordless phone base units come with a charger port for an extra battery. This allows one battery to be charged while the other is in use in the handset. When the battery in the handset dies, you swap it with the fresh battery from the base and recharge the dead battery. This feature allows the handset to be away from the base unit pretty much all of the time, and means that your handset won't be out of commission while you recharge a battery.

Hands-Free Headset
Some cordless phones come with a headset that plugs into a jack on the handset, and the handset is usually clipped to a belt. The headset has a microphone and speaker that receive input and output from the radio components of the handset. With this feature, you can talk on the cordless phone without holding it. Your hands are free to do anything else while talking on the phone, such as type on your computer, do dishes, work in the garden or play with your children.

Wall Mount
The base units of many cordless phones can be mounted on a wall so that they do not take up desk, table or counter space. This feature also has the advantage of keeping your base unit out of reach of small children. For example, my son can reach the base unit of my cordless phone, and his favorite activity is dialing numbers when we are not looking.

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Options
These optional features are usually available on the cordless phone, but, for the most part, they need to match your telephone service. Such options include the following:

• answering machine
• caller ID
• call-waiting
• two-line service

Answering Machine
This is the one optional feature that does not require a change in your phone service. Many cordless phones have an answering machine in the base unit. Modern answering machines are foregoing the traditional microcassette tapes in favor of solid-state memory. With solid-state memory, there are no moving parts and they can store 15 to 30 minutes worth of messages. Some machines also allow you to access your messages remotely with the handset or another phone.

Caller ID
This feature allows you to know who is calling you before you answer the phone. The number is displayed on the LCD of the handset and/or base unit. You must have the caller ID feature provided by your telephone company for this feature to work on your cordless phone. There is usually an extra charge for this service on your monthly phone bill.

Call-Waiting
If you are talking to one person and someone else calls you, call-waiting allows you to put the first person on hold and respond to the second caller or vice versa. Some newer cordless phones allow you to do this, but you must have the call-waiting service provided by your telephone company. Again, there is an extra charge on your monthly phone bill for this service.

Two-Line Service
This feature allows two phone lines to come into the same cordless phone. Some of these phones have two different handsets, while others use one handset to change between phone lines. This feature has the advantage of using one phone for two lines (personal line and business line, for instance) rather than having two different phones. Like the other optional features, you must have two phone lines installed in your house by your telephone service provider for this option to work.

In summary, consider the following aspects when looking for a cordless phone:

• frequency - related to range and security
• analog vs. digital - related to clear sound and security (DSS is the most secure!)
• convenience features and options - what you want in a phone to make it easy to use or to fit your individual needs

Choose from the map below:

When You Shop
We've created a Cordless Telephone Feature Comparison chart for you to use as you research various models. Take it to the store with you and fill in the blanks for each model you are interested in. You may also want to keep an additional copy near your desk as you research models on the Internet.

The feature comparison chart is available to you as a PDF. You will need the free Adobe Acrobat Reader to view it.

• Download the comparison chart!

Look Out!
When buying a cordless telephone, there are several things you should keep in mind to avoid buying one that won't meet all your needs. Here are some of the most important things to think about:

Security, security, security!
Because your cordless phone is a radio transmitter, it broadcasts signals over the open airways rather than specifically between the base and handset. Therefore, it is possible for other people to listen to your phone conversation by using a radio scanner. Digital phones are better than analog phones in this area, but DSS offers the best protection against eavesdropping. Low-end 43-50 MHz and 900 MHz analog phones are not secure. In fact, most baby monitors can pick up phone conversations from 43-50 MHz cordless phones. 2.4 GHz analog phones are rare (most 2.4 GHz phones are digital), but offer some degree of protection because most commercially available radio scanners do not extend into this radio frequency.

Many cordless phone conversations can be easily picked up by radio scanners

If your cordless phone does not have DSS, then your conversation is about as private as the writing on the back of a postcard. Use care when divulging private information over a cordless phone.

Think about the type of battery in your cordless phone!
All cordless phone handsets have a rechargeable battery (nickel-cadmium, nickel-metal hydride, lithium). Nickel-cadmium batteries are subject to a memory effect, so it is best to let them drain entirely before recharging them on the base. Nickel-metal hydride and lithium batteries have no memory effect.

Where to Buy

• Compare Prices of Cordless Telephones
• Super Deals

Popular Cordless Telephones
Here are some of the best-selling cordless telephone models listed for comparison.

VTech 2431 2.4GHz w/Caller ID	Uniden EXAI-378 900MHz w/Caller ID, Digital Answering Machine
Uniden EXP-2240 2.4GHz Analog	Memorex MPH6928 900MHz w/Caller ID
Panasonic KX-TC1743B 900MHz w/Caller ID, Digital Answering Machine	VTech 2461 2.4GHz DSS w/Caller ID, Digital Answering Machine

Manufacturers

• AT&T
• GE
• Panasonic
• Radio Shack
• Sanyo
• Siemens
• Sony
• Toshiba
• Uniden
• VTech

FAQ

• In the age of cellular phones, why should I buy a cordless phone?
  It is true that cell phones offer greater mobility than cordless phones, but cordless phones can give you communication freedom to move around your house or neighborhood at a much cheaper cost. Cell phone service is much more expensive than the basic telephone service used by your cordless phone. In addition, you do not have to purchase a separate plan to use a cordless phone as you do with a cell phone.

• Is it difficult to set up a cordless phone?
  No, it's so simple! Here's how you set it up:
  1. Insert the small end jack of the power cube transformer into the 9-volt DC jack of the phone.
  2. Insert the plug portion of the cube into the wall's electrical outlet.
  3. Insert one end of the phone cord into the phone jack of the phone.
  4. Insert the other end of the phone cord into the phone jack outlet on the wall.
  Lift up the handset, turn it on and you should hear a dial tone. You're ready to go!

• Is my cordless phone secure from eavesdroppers?
  Because your cordless phone is a radio transmitter, it broadcasts signals over the open airways rather than specifically between the base and handset. Therefore, it is possible for other people to listen to your phone conversation by using a radio scanner. Digital phones are better than analog phones when it comes to security, and DSS offers the best protection. Low-end 43-50 MHz and 900 MHz analog phones are not secure. 2.4 GHz analog phones are rare (most 2.4 GHz phones are digital), but offer some degree of protection because most commercially available radio scanners do not extend into this radio frequency.

• What is the best frequency for a cordless phone?
  Cordless phones operate over three major frequency bands:
  • 43-50 MHz
  • 900 MHz
  • 2.4 GHz

  43-50 MHz band phones have short ranges (about 1,000 ft or 300 m) and poorer sound quality (due to interference from structures and appliances). The 43-50 MHz phone signals can also be picked up easily on radio scanners and nearby baby monitors.

  The 900 MHz band provides a greater range (5000 to 7000 ft / 1500 to 2100 m), better sound quality and has more channels. However, 900-MHz signals can be picked up by most commercially available radio scanners.

  A 2.4 GHz cordless phone can operate over a greater distance and is above the frequencies that can be picked up by most commercially available radio scanners; so it is more secure than lower frequency models. A 2.4-GHz cordless phone will be more expensive than lower frequency phones.

  Higher frequencies will provide greater range to your phone and offer more channels for your phone to use.

• What's the difference between analog and digital?
  Analog signals tend to be more noisy, or prone to interference with respect to sound quality. In addition, analog signals are easily picked up and interpreted by radio scanner.

  Digital technology allows the phone signals to sound clearer and are more secure.

  DSS digital technology spreads the digital information in pieces over several frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on the cordless phone conversations. A cordless phone with DSS is the most secure.

• How many channels should I have in my cordless phone?
  Each frequency band (43-50 MHz, 900 MHz or 2.4 GHz) can be subdivided into different increments or channels. The base searches for a pair of frequencies (channels) within that band range that is not already in use in order to talk to the handset. So, if the base is capable of searching more increments, it can more easily find a frequency pair that is clear from interference. The number of cordless phone channels can vary:
  • 10 to 25 channels - 43-50 MHz phones, some inexpensive 900 MHz phones
  • 20 to 60 channels - most 900 MHz phones
  • 50 to 100 channels - high-end 900 MHz and 2.4 GHz phones

• How far can my cordless phone handset be away from its base unit and still work?
  The range of your cordless phone's handset depends upon its radio frequency, the type of signal (analog or digital) and the presence of interference. Generally, the higher frequencies will have more power to transmit and receive, and so will have a greater range. Digital phones will have clearer sounds over the same distances than analog phones. Interference from structures, appliances or other electronic equipment will affect the range. Under ideal conditions, you can expect the following ranges:
  • 43-50 MHz - about 1,000 ft / 330 m
  • 900 MHz - 5,000 - 7,000 ft / 1,500 - 2,100 m
  • 2.4 GHz - better range than 900 MHz, but exactly how much better is not certain yet
  If you use your cordless phone frequently when you are outside or taking a walk around the neighborhood, you may want to consider one with an alarm or indicator that tells you when you are out of the base unit's range.

• What type of battery is best for my cordless phone?
  Nickel-cadmium batteries are subject to a memory effect, so it is best to let them drain entirely before recharging them on the base; nickel-metal hydride and lithium batteries have no memory effect.

• Can I operate my cordless phone if I lose my handset?
  This depends upon whether your base unit has a keypad and speaker phone built into it. The built-in keypad in the base allows you to dial from the base to make a call even if you do not have the handset nearby. It is almost always found in combination with a speaker phone on the base. This feature keeps the phone usable when you have temporarily lost the handset.

• Can I have caller ID on my cordless phone?
  Yes, you can have caller ID on some models of cordless phones. The caller's number is displayed on the LCD of the handset and/or base unit. However, you must have the caller ID feature provided by your telephone company for this feature to work on your cordless phone. There is usually an extra charge for this service on your monthly phone bill.

  Some cordless phones can also have call-waiting or multiple line services, but your telephone company must set your house up with these services. Again, there are extra charges on your monthly bill for these services.

• Can I mount my cordless phone base on a wall?
  The base units of many cordless phones can be mounted on a wall so that they do not take up desk, table or counter space. This feature also has the advantage of keeping your base unit out of reach of small children (my son can reach the base unit of my cordless phone and his favorite activity is dialing numbers when we are not looking).

Cool Facts

• Your cordless phone is a radio transmitter and receiver!

• Most baby monitors and walkie-talkies can pick up phone conversations from 43-50 MHz cordless phones.

• Digital spread spectrum (DSS) was invented by actress Hedy Lamarr.

• Cordless phone components are getting smaller, which means that more and more functions can be placed in phones without making them any bigger.

• Memory chips, instead of cassette tapes, are now being used on cordless phone answering machines.

Lots More Information!

Related HowStuffWorks Articles

• How Telephones Work
• What does 900 MHz mean in a cordless phone?
• What is digital spread spectrum as used in cordless telephones?
• How Radio Scanners Work
• How Radio Works
• How Cell Phones Work

Buyer's Guides

• Deja.com: Cordless Phones: Buyer's Guide
• Amazon.com: Cordless Phones: Buyer's Guide
• Active Buyers Guide

Reference

• Cordless Telephone History
• Epinions: What does the difference in frequency mean to the cordless phone buyer?
• ConsumerReview.com
• ConsumerSearch.com
• 1995 FCC Report: New Cordless Phone Frequencies
• Cordless Phone Digital Security
• Cordless Phone Spread Spectrum
• 1993: High-power digital AT&T cordless phone has one-mile range
• Court case: recording of the cordless telephone conversation
• Can other people listen to my cordless and cellular phone conversations?
• Cordless Modem