Thanks for all of your replies, but how does it work electrically. How does the blade sense it is touching a finger or meat or a wet material?
They charge the blade and constantly measure the amount of capacitive charge on it. As something fleshy approaches, the capacitive charge on the blade begins to discharge toward the "flesh" and by the time it touches, the trigger process has already started so it can act very very fast. The "hot dog demo" they use by the way only works because the person is holding the hot dog with their bare fingers. If you put the hot dog on a stick or held it with non-conductive gloves and pushed it in to the blade, it would be cut off because the hot dog cannot absorb very much charge.
We had one at a shop I worked with and messed with the newbie shop workers on it. We would start by having them wear latex gloves on shop training day (supposedly to protect their hands because they didn't have callouses yet) and then show them how it would stop for us with the hot dog. Then we would replace the cartridge and hand them a hot dog to try it. The latex glove however would insulate the hot dog from their capacitance and they would cut the hot dog. We would tell them that it must detect them as newbies and to NOT use the table saw without supervision. We would explain it to them a few days later...
I have heard, but not witnessed, that it can be falsely triggered by very green wood being held by a bare hand, but a false trigger, while costly, is still better than NO trigger when it really is a finger.