When I was working in the Police Department, my immediate superior and go-to guy in my Unit had this frickin' awesome exacto'ish small blade that you could attach to a key -- and still have that key be completely functional without having to take off the blade. I have no idea where the hell to find one, but I had a bit of a weird experience going back to my car in a dark alley two or three nights ago and I want that shit for personal protection, because I'm always ready to do a key-to-the-carotid going to and from my vehicle.