Before to find spy camera, you need to know that there are two types of hidden camera in the market, wired and wireless miniature spy camera. The major way to detect the pinhole spy cameras; through light or through radio frequencies (RF).
Every camera has a lens that reflects light. You can turn on the smart phone camera (flash light off) and check around the room to see if there is any red dot. If yes, there may be a pinhole camera. (Make sure, there are no mirrors, glass or other reflective surfaces in the room)
Remember, some of the smart phone has infrared filer that cannot see the red spot.
According to the testing result, you need very close to the target and the angle of phone and spy camera need to be the same it order to get the reflections.
More secure way to find spy camera is to use an eavesdropping detection device - Camera Lens Detector. The lens detector has a series of red LEDs around a lens that you hold up to your eye. They generate what are described as “sparkling red dot” when they detect what appears to be a camera lens, so you can investigate further.
For the wireless spy camera, it does transmit radio frequency, you can use RF Detector to check if there is any unusual transmission signal in a room
Regarding to video transmission, there are analog and digital signal.
To detect analog wireless spy camera, likes 1.2 GHz, 2.4GHz or 5.8 GHz hidden camera, you can use Camera Hunter or Camera Interceptor which can locate and display video on monitor.