I don't believe in the "Magic Wand Theory" of personal protection. 

 Unlike on TV, the black thing with the hole in the front and a handle on the back is not a "Magic Wand".    It doesn't make everyone run away or to do what you want them to do.

If you aren't prepared to actually use it to kill someone or don't know when you are authorized to use it you are a) likely to have it taken away from you and used on you instead; or b) likely to use it and be in jail yourself for doing so.