"Where's My Droid" for Other Bluetooth Devices

Modern smartphones have very nice "find me" apps, that cause them to turn the volume up to max (even if on silent) and ring when you send them a special code. Very, very convenient. It would be great to have this kind of capability with other devices. The way I can envision it working is that your other small, electronic devices--car keys, wireless headsets, iPods, etc, etc--have either Bluetooth or maybe RFID. They might not actually be able to "ring" on their own, but at least they could play "hotter/colder" with your cellphone, to clue you in if they are nearby and you are getting closer.