Magicfly Wireless RF Item Locator Key Finder 1 RF Transmitter and 6 Receivers
Just having recieved it,  I cannot really attest to its performance but it does seem to work as advertised.  As others have noticed, it wold be nice if the signal were a little louder and lasted a little longer.  Finally, the  little rings that attach it to your key ring should be larger and easier to use.