K.I.S.S
The remote transponder key thing is a reasonable idea, come mountable alarm, you could have them on your wrist or anything really...the chips are small enough...look at Proximity access cards..work on a similar principle.
But, my initial response still stands... K.I.S.S.
Oh, and a mobile telephony "Cell", is I think, the area intersected by 3 transmitter radii, so if you have 3 transmitters, near to each other, each with a 50 mile radius, they will find the phone with one, then use the other two transmitters, that overlap, to locate a small area where the phone is.
You can actually, pay a subscription, to be able to locate a phone, within a small area.
It's designed for parents to monitor their kids "suposed" location, and sends you back a text with a picture of roughly where they are.
How about a quick connect, over the shoulder strap, you can clip onto your gat, so you can sling it on your back, quickly and easily, so you dont NEED to leave it laying around?