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Simply using a cell phone is now a givaway, a Russian soldier was zapped recently when he used his phone to boast of the destruction he had caused;
'Devices called cell-site simulators, which mimic a phone mast, are stationed inside drones and trucks and sent over the battlefield to pick up the signals of nearby phones.
The simulators trick the phones into measuring and reporting the strength and direction of the signal from several phone masts in the area.
By analysing these responses – whether the signal is stronger or weaker with different masts - it is possible to find out where the phones are likely to be and send in an artillery strike at that spot.
It is also possible that some systems can directly identify the phone's location when the simulators connect to them, for example by accessing the phone's internal GPS system.
Whichever method is employed - and the finer details are closely guarded military secrets - they all end with the enemy obtaining a reasonably accurate location of whoever is using the phone.'