If you are afraid that you or someone you know has been recorded by a secret camera, you can use the Third Eye - Spy Camera app to check for the presence of any hidden devices. This app works like a magnetometer, it detects any magnetic field and gives you an indication of the presence of a camera or other electronic devices near your location. However, you need to have a magnetic sensor in your phone to use this feature. This app can also detect infrared lights which also indicate the presence of a hidden camera.

The app is extremely easy to use. The first thing you need to do is install it. After that, you can just run the app and move your phone close to suspicious spots to check if there is any hidden recording device.