There must be a hidden mechanism in the chamber for opening the door from inside.

The female touched the wall; a small spring depressed, releasing a hidden mechanism.

Behind the wall was the hidden mechanism that operated the defenses of this meeting room.

Then a vague grinding sound, as some hidden mechanism deep within the small world began to function.

He found the gun after his fingers had located the hidden mechanism of a secret drawer.

He turned abruptly to the wall of the room, pressed a hidden mechanism.

She heard a low click, as if some hidden mechanism had just snapped open.

There must be some kind of hidden mechanism designed to trigger the door.

Bob must have touched some hidden mechanism that opened it.

He manipulated a hidden mechanism that opened a panel in a side wall.