I wonder if you've read Fallen Dragon by Peter F. Hamilton? Unremovable, remote controllable lethal necklaces are a central plot device in the mercenary invasi

I wonder if you've read Fallen Dragon by Peter F. Hamilton? Unremovable, remote controllable lethal necklaces are a central plot device in the mercenary invasion. They are put on randomly chosen civilians as "collateral" to ensure co-operation and disincentive insurgency.