How do the sensors on restroom paper towel dispensers work?

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I know there’s different makes and models but I’m talking about a certain one. I’ve seen different dispensers do this too. It won’t actually dispense more paper until you rip off what’s hanging down despite having the wave sensor on the front of the machine. I’ve managed to screw around with one once and trick it into dropping more paper without me tearing it off but there’s no sensors I can see or feel on the inside. The only sensor is the one on the front with the image of a waving hand which some dispensers will dispense with the wave of a hand but where I live the majority will only do while it tears. It’s like the wave sensors were rewired into some kind of tearing sensor. Someone explain it.

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Anonymous 0 Comments

The sensor is on one side of the paper and the receiver is on the other side of the paper. When there is no paper it is waiting for your hand to reflect the light back up to the sensor. When paper is hanging down it blocks the beam from ever reaching your hand, so there is no light to reflect back to the sensor.