There are some ideas that are inherently patentable.
SawStop, applies a small electrical current to the blade of the saw. This current is continuously monitored. If the saw detects a change in this current (as would occur if a hand or other body part came into contact with the blade) an automatic braking system is activated, forcing an aluminum brake block into the blade.
The saw stops within 5 milliseconds, and angular momentum lowers the blade into the table. The operator suffers a small nick rather than a potential amputation. The process does ruin the blade, however it’s a small price to pay for saving a finger.
I saw this a while back, and like yourself, felt amazed enough to post about it. Check out the video I posted, the inventor puts his money where his mouth is and tests it on his own finger!