Don't know if the seat belt cutter works. That's why I'm giving four stars instead of five. I bought one for each car/family member and thought - wait a minute - how do I know they even work? So I went to the junkyard and they had me break three side windows of the car. (NOTE, I have not tested this device on a windshield. I don't think it will work on a windshield as the glass has been specially treated not to shatter if the windshield breaks on a freeway or similar.)