Davis has a good posting about how you can use your cell phone as a defensive weapon.

But of course, it’s not quite what you think. 🙂  Quite a good strategy for what he’s getting at however. It reminds me of those gadgets you can keep in a pocket. You are entering some situation you don’t want to deal with, slip your hand in the pocket and press a button on the gadget. In a couple minutes the gadget will go off, like a cell phone ring or a pager or some such thing and then oh, I’ve got to take this, sorry, gotta end the conversation with you or I need to leave the room to take the call or whatever. Amusing.

Still tho, there is potentially a bit of serious self-defense application here. The key point is being aware of your surroundings.