There are two ways to find the hidden cameras.

1. Some hidden cameras use infrared fill light. You can find the camera by checking whether there is infrared light. But at present, there are no mobile phones that can sense infrared light. So this gadget that specifically senses infrared light is a choice.
2. Camera lens detector. All these lens finders work with the same principle: a red (often flashing) LED light is directed at the suspected location and if there's indeed a camera lens there, you are able to see the reflection of the LED light on the lens through a filter. However, if you're using it to inspect a hotel room, this kind of way is inefficient, and you'll need to search the room area a little bit to make sure you don't miss any flash lights. In addition, the flashing red light can cause rapid eye fatigue. That means it is effective but painful.