What Is External Caller ID?

By Nick Davis

External caller ID devices come in a variety of sizes from a number of manufacturers.
i Ryan McVay/Photodisc/Getty Images

An external caller ID device connects to your landline telephone connection and informs you visually of the number that is currently calling you. The devices include a LCD display and which also shows the caller's name, date and time of the incoming call. An external caller ID requires you to have a subscription through your area telephone service provider for caller identification service before the device can work.

Additional Features

External caller ID devices also include a built-in memory component that stores telephone numbers, a mounting bracket for attaching the device to a wall or other surface, and indicators that inform you of incoming calls. The device's memory capacity varies from model to model. External caller ID devices also include the ability to select English or Spanish as your preferred display language.

External caller ID devices are also available that can display an incoming call's number when you are using the phone. This devices are known as "Caller ID-Type II" and "Enhanced CallerID." This feature works with the call waiting feature and also requires that you subscribe to the call waiting service before the device can process the caller information.

Electrical Requirements and Display Exceptions

The devices require "AA" or "AAA" batteries; some external caller ID devices contain an AC adapter. Check your caller ID's documentation for specific battery type and if an AC adapter can be used with the device. Not all incoming calls' phone numbers will display on your external caller ID device. If the number is blocked, a cellphone number, a long-distance number or private, you may see the following words on the device's LCD display: "unknown," "out of area," "cellular," "private" or no information at all.


External caller IDs are available at retail, electronic, hardware and home improvement stores. The devices are also available from your telephone service provider, online electronics and telephone accessory outlets and online auction websites.

Connection Information

The devices include two telephone jacks -- one that accepts a telephone extension cable from the wall jack and one that accepts a telephone cable that connects to your telephone. The jacks are labeled "Line" and "Telephone" or have a picture of a telephone jack and one of a telephone.