Magicfly Wireless RF Item Locator Key Finder 1 RF Transmitter and 6 Receivers
Good value, with enough to keep track of two keys for two cars.  Worked great at first, and I had given it 5 stars, but now it has stopped working.  The problem is in the base unit, apparently: none of the tags will receive a signal from the unit, even when I checked, then changed the batteries (which were still good).  I'm not sure what happened, but now it's useless.