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Those worked by sound. No power was needed or generated by the remote.
From the article…
By pressing a button on the remote, you set off a spring-loaded hammer that strikes a solid aluminum rod in the device, which then rings out at an ultrasonic frequency.
I THINK I even remember, way back, random channel changes from tapping on a drinking glass or something similar… Cool tech for the time
It works. Been using it without fail.