People normally do this by scanning a 10mW 832nm laser with a mirror, according to Dan Gelbart in https://www.youtube.com/watch?v=0MtRxX0crjU. The lecture is 77 minutes, covering nonlinear junction detectors, digital calipers, the US-embassy bug in Russia, laser microphones bounced off windows, and geometric errors from material relaxation. The bit about camera detectors is close to the end. Works for eyeballs too.

Lensless sensors (for example, using compressed sensing, or Hadamard shadow masks) can presumably defeat this, but also, watching from far enough away should defeat it. Hard to do that inside a pervert's AirBNB, though.

Definitely trying this next time I check into an Airbnb. The old flashlight trick is tedious.

Finally, a practical use for those notification LEDs. Definitely adding this to my travel toolkit if it proves reliable.

Until someone develops hidden cameras with AI that will be auto turned on couple of hours later after detecting presence at that time a scan was already performed and nothing was found.....

Using the phone's existing LED for this is clever. Wonder if the 'AI' is genuinely learning or just a sophisticated reflection analysis.

Wonder if it handles the really tiny pinholes effectively. For now, a thermal camera feels more robust for peace of mind.

If this worked with IR, and so non visible, it might be even more useful.

Great idea though.

Another strategy that's often used is to cause motion then detect the resulting transmission spike. That's also defeatable of course (cache+burst, CBR, etc).

The ideal detector should incorporate multiple methods. Someone should make a site that rates these for each detection method then adds them into an overall score.

I wonder if it works with smart glasses.

Can't a thermal camera can do this? It should be able to detect any difference in ambient temp, even a few degrees, and a CMOS sensor gets warm, not to mention any wireless transmitters, power sources, and ICs. Turn off everything in the room and walk around with a ~$100 ali express handheld thermal camera.

Cool, but we need that for microphones.

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Yeah I don’t think this will be effective, cameras can be put in certain angles that it can see with being seen, or how police do it, entirely behind clothes or similar fabric where it can see through and identify but not seen even if you’re looking straight at it.