How Does Caller ID Work?

in Technology

Did you know that Caller ID, the amazing little technology that we now take for granted, has been around since late 1988? Caller ID is so popular now, that some people couldn’t imagine answering the phone without knowing who is on the other end. And some people won’t at all!

We’ve become so familiar with Caller ID that we don’t even ask how it’s possible. So for the rest of us curious users, we’d like to know, how exactly does caller ID work? It turns out that the technology behind the process is quite simple, despite the 20 patents it took to get caller ID up and running. The technology is similar to how modems work. The early modems used a technique called Frequency Shift Keying (FSK), which would transmit bits over a phone line. FSK is a simple concept, one tone represents binary 1, while another tone represents binary zero. Binary code has dated back to the 17th century, but was first used in computers, and the modem will change frequencies depending on whether it needs to send a 1 or a 0. How quickly it changes frequencies will determine the speed of the modem.

Now, on to Caller ID. Caller ID information is sent through the same FSK technique that is used with modems and it sends “ASCII” character data to the recipient’s caller ID box. ASCII includes 128 characters, 33 of which are control characters and 94 are printable. The information is sent after the first ring and sounds like a quick “bleeeep” that lasts for only a half a second.

If you were able to decode this bleep, you would know that there is a series of alternating 1s and 0s being. There would be one byte representing the type of message, one for the length and two representing the exact time, down to the minute. Lastly, you would know that there are ten bytes being transmitted that reveal the ten digit number that is calling you. If your caller ID box is more advanced and displays the name of the caller, then there will be more ASCII characters being transmitted. Essentially, your caller ID box contains a little modem, which can communicate with other technologies.

Compared to the high-tech gadgets we have today, caller ID may not seem like advanced technology, but there are constant add-ons and improvements being made. They now have caller ID blockers, call spoofing, star 67 and caller ID descriptions, all of which would not be possible without the original caller ID technology.

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Dave Smith has 99 articles online

About the Author: Dave Smith is a Marketing Associate at Itellas, a leading provider of caller ID spoofing services. For more information about call spoofing, please visit

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How Does Caller ID Work?

This article was published on 2011/10/03