There's a similar thing in one of the Mission impossible movies
as no one would volunteer for a bomb in the head, he'll tell them it's an RFID chip needed to open doors or access security or somesuch
With a heart monitor built in so emo can tell if they're in distress & send help
So if their heart stops, device is removed, they get out of range etc... the device explodes
Then it just needs to be externally addressable