You asked what a Saw Stop is. It is indeed expensive, but it will save your body parts. In a nutshell, the blade gets a sensing mechanism that knows the difference between flesh and wood. If you cut wood, the saw does its thing. If your finger gets in the way, the blade stops instantly, before your hand/finger/body part is removed from the rest of you. They are for real and they work.
A factory rep called these saws, "The Weenie Saw". He would run an uncooked hotdog into the blade and the blade would stop before cutting through the hotdog skin. Expensive demo though. Had to replace the brake pads after each demo.