Prevent stealing of Mobile Phones

Very basic way to keep your cellphones safe is to tie it to a Retractable Key/Card Holder that you lock into belt loop from inside the trouser's pocket. No big deal to stitch safety hook inside the pocket thats strong enough to not tear. 

Courtesy link: SNAPDEAL.COM

But what if you can still go electronics/tiny area radio signal way?! If your phone moves away 2 feet from your radio signaled detector/bluetooth, hidden somewhere in your body, then the phone beeps loud even if its silent mode! You catch the thief. If the real owner have to pick up the phone, s/he can type in the password to nullify detection for the moment.

OR....There must be some way of the mobile phone detecting a hand by it's pressure, or position or skin print within 10 seconds of anyone lifting it. If its not the true owner that has picked the phone, it's internal security should generate high pitched siren!! 

Or even, if skin or pressure detection is not possible, there must be a way to detect its been picked up and if the true owner doesn't type in the pass code, the siren goes off!! Imagine someone picking your pocket in a bus? Can he really get away without getting caught?! :)

Why shouldn't I be awarded a cash prize for my