How to detect HIDDEN CAMERA in trial rooms..........

How to detect HIDDEN CAMERA in trial rooms..........     In front of the trial room take your mobile and make sure that mobile can make calls........ Then enter into the trail room, take your mobile and make a call..... If u can't make a call......!!!! There is a hidden camera......    This is due to the interference of fiber optic during the signal transfer......     Please forward this to your friends to educate this issue to the public...... To prevent our innocent sisters and ladies from HIDDEN CAMERA............