This is how you can find hidden cameras (even the ones without lenses) with a few light flashes. Researchers came up with a surprisingly effective method they call Eye of Sauron. Just rapidly switch the lights in a room on and off. When the scene changes abruptly, a camera’s codec has to re-encode a lot of new data, which spikes electromagnetic emissions from its memory controller. If you sync the flashes with an EMI scanner, you can pick up this signature and locate the camera - even pinhole ones that only record to an SD card or stream over a cable. In their experiment with 50 different camera models, every single one was detected after just four scene changes. Some were found more than 20 meters away and even through walls. Detection range reached ~30 m for plastic-cased cameras and ~11 m for metal ones (far better than typical commercial detectors that only work at 1–2 meters). The whole scan took between 4 and 32 seconds depending on room size. The method nicely complements classic RF scanning and looking for lens reflections. They also used radio-astronomy filtering techniques to cut through the usual household noise (phones, routers, kettles, etc.).