Use bug detector
The most reliable way is to use a bug detector. These can be bought easily from an electronics store. Their basic purpose is to locate the radio waves that are being emitted by any equipment in a given room. In this way, you can easily know which room has the surveillance camera or the place where it is installed.
Search in ceilings and around light fixtures
Most cameras are installed in areas where most of the room can be seen which means with the best overall view. Ceilings should be the first place where you should be checking for. You must check through all smoke detectors and around the light fixtures. Look for any patches that have been painted or covered recently.
Look for red or green lights in the dark
Another way is to look for red or green lights in a room after turning off the lights. These are power indicator lights in most devices but they are very difficult to track as you may not easily see them. Use a flashlight to check corners of the room.
Go through all wires in the room
Perform a quick check on all the wires that are in your room. You need to check whether there are any wires that you do not need and are still there. These may be connections to the equipment.
Thoroughly check lamps and picture frames
Perform a thorough check on all the lamps and under their covers. These are also a very common place of installing a camera. Also, closely look through any paintings in the room.