Comment by ars
A timer is too risky. The was done months in advance - what if the war was over?
I think this was meant for intelligence gathering - now that they know who the important operatives are, you go backwards using video and see where they went and who they talked to.
Seems easier to install a transmitter and GPS in the supposedly receive-only device. Then it could actually track people and show where they had been. It could store up readings and only transmit while the device was in motion at around walking speed, with signal strength above Y. That means the person was probably outdoors and moving, thus probably ot being swept by bug detectors. Well maybe not any more, now that everyone is thinking that way ;).