spy detection

“What about the girl? If you want a bed for her, you should ask for one sooner rather
than later. You headed across Eurasia, so you should know. We’re in a war here. There’s
no guarantee that there will always be an open bed.”
“...It’s true that carrying her around while fighting is rather stupid. Given her condition,
it may very well be better to throw her in a hospital. But...”
Suddenly, Accelerator pulled a handgun out from his belt and shot out the legs of a
different nearby soldier.
The white soldier was unable to react to the sudden action by the person he had just
been speaking with.
Meanwhile, Accelerator shot out the legs of two or three more men and women within
the room.
“They were spies,” Accelerator said languidly. “If I’m gonna leave that brat somewhere, I
need to make sure it’s a nice clean environment.”
Accelerator lightly kicked the first man he had shot who had collapsed unmoving to the
floor. A tiny microphone similar to what a performer would use fell from his clothes and
it was connected by a cable to a medium for recording and transmitting. The actions of
the Elizalina forces were being monitored by the Russians. Or perhaps, they were using
advice and false information to lead the Alliance astray.
The white soldier hurriedly checked the pockets of the others Accelerator had injured.
Similar devices were found hidden on them.
“The range of those transmitters is low. Most likely another spy has a real transmitter
outside.”

- Toaru Majutsu no Index Volume 21, Chapter 5 Part 3