These days, there is a lot of concern over privacy issues and worries about hidden cameras. This app can detect a hidden camera efficiently. (You need to have a magnetic sensor in your phone, otherwise this will not work.)
Just fire the app and then move your phone close to the area where you doubt there is a hidden camera—it could be a shower, flowerpot, lens looking part or changing room mirror. If a camera is detected, it will beep instantly.
It also has one more tool which detects infrared lights. Just open the infrared detector and scan for white light that appears on the screen but is not visible to the naked eye. Such white light indicates infrared light. It could be an infrared camera.
A very useful tool while travelling or in changing rooms.