This is SawStop, it's a saw that could save you from a serious injury. It works just like any other table saw, but stops immediately when in contact with flesh.
It works using the electrical signals from your finger. These signals are picked up by the saw blade and trigger the brake cartridge underneath.
This cartridge springs upwards and stops the saw almost instantly. Both the blades and brake cartridges are easily replaceable.
Read more: http://www.businessinsider.com/sai