If you suspect you're being watched via a hidden camera somewhere in your house or private space, your Android phone is a useful tool for detecting certain types of surveillance equipment. Although not fool-proof, it's possible to use your Android phone's camera and magnetometer sensor to detect hidden cameras and microphones, or other listening devices.
How to Detect a Hidden Camera Using Android Camera
Some hidden cameras emit IR (infrared radiation) light, which isn't visible to the naked eye. The camera lens on your Android phone will pick up infrared light if you hold your device close enough. If you find a hidden camera that emits IR, it will appear in your camera's display as bright white.
Launch your phone's camera app.
Go around the room and point your phone's camera in areas you suspect spy equipment is hidden.
A screenshot showing IR light from a TV remote with Android's stock camera app.