There was a long conversation about on rec.woodworking newsgroup. Basically there is some kind of capacitive pickup on the blade that can detect "meat". When it triggers the blade is forcefully retracted and slammed against a brake material in a fraction of a revolution. It usually trashes the blade and the whole saw stop mechanism may need to be replaced but you will have all 10 fingers to do it with.
Your blade is toast,and as said in another post, the cartridge does need replacing too,I'll pass on that import machine & keep my old Delta saws, there is not much of a sub. for being aware that your blade will eat your finger(s) just as EZ as wood & acting accordingly.....
When the device triggers, the blade is history. What happens is that, essentially, a bullet is fired into the side of the blade, pinning it against the mechanism. The blade is now permanently part of the cartridge. When you replace the cartridge, you are able to install a new blade.
There may be more on how the sensor works out there now but it was proprietary "magic" when these things first came out. It does seem to be able to figure out the difference between a hot dog and a wet stick but one of the guys who had them said he did have a false trigger. I am not following rec.woodworking these days but it should be easy to get a thread started if there is not one on there now. Guys are passionate for or against these things. It is sort of like 4 stroke outboards vs Etec or "classified breakers". Easy to start a fight.
The manufacturer of the device had encountered some opposition from various saw makers in the adoption of his device. According to him the saw makers feared that any actions taken to adopt the device, or even acknowledge its' existence, would become fodder for lawsuits.
That has changed in the past few months, and several saw makers are looking to incorporate the device in at least some of their models. These other models are not yet available (AFAIK), so you are still limited to buying the model produced by the device maker.
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.