Quote:
Door Openers and Alarm System Motion Detectors run off of Inferred
They see a difference in heat from the previous measurement
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Many commercial door openers back in the day used X-band radar for motion sensing. Used to set off the radar detector from a 1/4 mile away from supermarkets and the like.
I haven't used a detector for almost 20 years, so I can't comment on what's currently in use, but I can confirm that radar frequencies were in use previously for this function.