Right after the tragedy of 9/11 it was almost impossible to know what was and was not allowed on airlines. Even luggage that was checked into storage had restrictions that made no sense to anyone, and it seemed to change from day to day.
However, the Transportation Security Agency (TSA) eventually managed to pull together a coherent list of what is and is not allowed aboard a plane.
While the “on board” carry list is still highly restricted the good news is that if you want to take your pepper spray or stun gun in your checked luggage you are free to do so. You do not even have to notify the TSA or your airlines. Please note that there are still size restrictions and limits on self-defense products that use tear gas.