That's a really interesting idea.
I would buy one. My dog was stolen from me (I had her tied up outside a store, and when I came out she had been taken). Witnesses helped me track down the thieves (just some crackheads) and I got the dog back... but I was very very lucky. I would love to implant something like this in her.
I would imagine that kinetic energy could be harnessed to power the unit.
And for those who are wondering: Yes the thieves took her collar off immediately. That was probably the first thing they did, I found it on the ground.