Regardless of all of the technical arguments about RFID range, the idea behind this product is that it beeps, so you don't need fancy locating equipment. I don

Regardless of all of the technical arguments about RFID range, the idea behind this product is that it beeps, so you don't need fancy locating equipment. I don't know of any passive RFID tags with enough left-over power to run a loud beeper. You would need a strongly directional antenna and user input (or an antenna array) to find the tag using the phone itself, which would be a relatively bulky and expensive piece of equipment. If you're just trying to find something using radio, a 100% passive system like http://en.wikipedia.org/wiki/RECCO http://en.wikipedia.org/wiki/RECCO is simpler and cheaper anyway.