KeyPS is a bluetooth enabled device that attaches to your keychain, and connects to your mobile phone via bluetooth. The device itself is the size of a quarter, and about 5.5mm thick, very sleek, and hardly noticeable unlike other competitors products.
Uses RSSI to estimate distance from your mobile phone, with a built in buzzer for short range. (i.e. in the couch). As well, if you go out of range, the app will log the GPS location, and allow you to retrace your steps, and find them.