Zap?
I know, there's an iPhone application for everything these days, but this one reminds me me of the 'Fire Extinguisher In a Pen' that came with a supply of burn ointment—except this gizmo doesn't come with ointment.
The better Oleoresin Capsicum (OC) pepper sprays can buy you some precious time to get away—but you have to stay in contact with the attacker for this thing to work. What then? You might wish that you had some ointment!
-fl