remote telephone locator?

I am searching for the right terminology or names of parts involved in the following. In cordless phones there is a device that allows you to push a button on the base unit that will trigger an audible beep to tell you where the phone is. I would like to know what the names of the componants are, button I guess would be some kind of transmitter and the phone itself would have some kind of reciever that allows it to beep.

Cordless phones obviously already have transmitters and receivers to broadcast the phone ring and voice signals from the base station to the phone. They just use the same circuitry to broadcast a signal that causes the phone to beep.

Ok... I do understand that part. But I want to be able to build or create that without all the phone parts. Which I probably was real clear in my first post. I want to build a device that is about the size as the remote unlock device for cars with a receiver that beeps thats as small as possible. Does that make sense? Where could I purchase those parts and what would they specifically be called?

Do searches for "remote control modules" and/or "remote control key fobs".