From what I read they send a small electrical charge through the blade, since wood has low conductivity its fine. When it hits a finger or hot dog the electrical sensor goes nuts and blows a fuse. Destroys a blade and the enclosed aluminum block - $170. I for one would gladly pay that knowing that I saved a finger. Now if only they had a retrofit for my Craftsman saw. What really is amazing is that they are building prototypes for band saws, mitre saws and even circular saws.