The three fingered wood shop teacher may be stereotype of the past. The SawStop table saw blade has a small current running through it. Whenever an unfortunate finger or wiener comes in contact with the whirling blade, it changes the electrical resistance enough to cause a sensor to trip a spring loaded aluminum brake, which stops the blade and uses the blades momentum to carry it back and down out of harms way so fast you would barely need a band-aid (1/200th of a second).
Erika from Hot For Tools will run you through a demonstration. So far the feature isn’t available in existing brands, so you have to buy the Sawstop saw. The stop mechanisms aren’t cheap enough to make you want to show off the feature in action to your friends, but they are a whole lot cheaper than an emergency room visit, regret, or for you employers out there, workers comp adjustments. As Erika showed us, this saw is sold by ToolKing here:
SawStop Table Saws at ToolKing