I would assume that the additional resistance of a finger is fairly negligible compared to the density of hardwood or metal
In: Engineering
Contrary to most answers here. Devices like SawStop use captive sensing not resistive.
Simply touching the blade does not make you part of any circuit. Doing so would also be a safety risk since any malfunction of the device could send more current down your body than is safe.
Instead they use captive sensing. The circuit monitors the capacitance of the blade and when something with high capacitance is added to the blade it can be detected without any significant current passing. The blade has a known capacitance that is tested when powered up. If that changes say more than 10%, fire the safety mechanism. [Here is a tutorial if you are curious.](https://playground.arduino.cc/Main/CapacitiveSensor/)
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