Lost key finder?

Has anyone ever attempted to make a lost key (or other object) finder system? I've had one in the past: you attach something to your keys, and then there's a remote. If you push a button on the remote, the object attached to your keys will beep so you can find it. Limited range, RF I'm guessing.

If you have built something like this, what did you use? If you haven't, what would you use?

Thanks!

Two of these wireless transceiver would do the trick: RFM12B-S2 Wireless Transceiver - 915MHz - WRL-12031 - SparkFun Electronics

and they are quite cheep!

Also you could be interested by this thread: Whistle detection - Audio - Arduino Forum

Good luck XD

Francois