Well. They are Booby Trap Alarms according to his Youtube video title but you could modify the design slightly and come up with something that undoubtedly violates some law here in the United States. Royal keeps it legit and has designed a trip wire notification device that uses cut down 12 gauge shot shells to let you know if someone has breached whatever perimeter you have established.
Royal’s videos are always interesting and I like that he has stayed true to his roots as a home built gun enthusiast even though he has received some flack for it over the years. As always, his design looks like it was built by some sort of super intelligent monkey, that also happened to be drunk.
It is quite simple and should be easy enough to replicate if you want one of these of your very own. The guides and mounting point are all standard nuts, the striker and shell holder are nothing more than some tubular steel stock, and the spring is pretty common as well. All you need to bring the design together is a small amount of welding talent, preferably with a high amount of experience in booger welds, and some time.
Check out Royal’s video below, his channel is chock full of great home built projects.