An evil cellphone factory distributed cellphone units that can cause instant death to a human. It was distributed to every adults in this world.
The units will kill its owner by the ff reasons;
- The phone died/destroyed.
- Dismantling the phone.
- The phone is not in the possession of its actual owner.
The units allows the owner to receive announcements from the factory and detect nearby owners.
Given these information the factory said they will trigger the instant death to everyone who owns the unit within a year and the only way to prevent this is to destroy half of the distributed units.
What can be the most realistic explanation on how will the phone kills its owner?
Edit: I am looking for a way that doesn't allow the owner to survive if the phone triggers its death killing procedure.