His sensors told him their defense shields were in place.

Internal sensors would tell whether they were following or not.

But the room's sensors would tell his captors if he moved.

And his sensors weren't telling what he needed to know, either.

"Now what can the sensors tell us about this little mystery? "

By measuring the time needed for the response, a sensor on the ground can tell how far away the plane is.

"But my sensors tell me that neither of you is human."

"What do our sensors tell us about the technology of this civilization?"

His sensor told him Claudia was on the second floor.

Your sensors must be telling you the same thing mine are.