Cellphone Anti-theft Button!

Hi Nokia/Samsung/Motorola

I thought of this tiny invention long time back and was reminded of the same just yesterday while looking at those bluetooth headsets.
It's about a bluetooth gadget - a tiny one that can be hoked onto button of a shirt or handbag or anything with a beeper which will beep whenever the mobile is out of a pre-defined radius, say 1meter, 5m or 15m depending upon kind of job person who is using it. This shall alert the user when his mobile is getting at a distance from her/him for any reason thus drastically reducing theft cases.
Idea is that mostly people loose their mobile out of inability to keep track of it all the time, especially in crowded places or during busy schedules and if something like our gadget can remind them on getting away from cellphone, it can immediately take them back to it.
The gadget can be either a part of the headset or a standalone gadget itself, latter being preferable as not all the time is one supposed to carry the headset and not everyone like to use one.
The same shall do demand getting used to carrying the button every morning or evening whenever one is moving out. Also, it shall demand bluetooth (or any other technology) to be active all the time.