As has been stated, check your laws before you carry it. If anyone traces your carry to this thread, they have the means to show your intent that it was for self-defence... which means you carry it as a weapon. In CA, it would be a felony.

That means as soon as you have it in your hand during an engagement with a person*, you just gave him justification to shoot you. Dead. End of story.

If you hit someone with it, you could be charged with Assault with a Deadly Weapon (CA).

Pretty neat though, huh?

Get real. If you want to use sub rosa devices for self defense, get something that won't get you arrested or shot in the first place.

EDIT: *Unless you are using it in response to a threat of deadly force.