However, if you are looking for something unique and more useful, the Yellow Jacket may be for you. Currently pitched in an Indiegogo campaign, the Yellow Jacket is a case that turns the iPhone 4/4S into a 650,000 volt stun gun. The inventor claims that the charge is plenty to incapacitate an attacker temporarily. And since it is attached to your phone, there is a good chance that you will have it handy at all times.
The Yellow Jacket carries its own circuitry and a massive battery that triples the thickness of your phone. It's not exactly elegant, but it is more compact than if you had to bring along, for example, an extra Taser stun gun. Plus, Yellow Jacket says that the battery provides up to 20 hours extra running time for the phone.
At the time of this writing, Yellow Jacket had collected about $26,600 of its $100,000 funding goal. There are 13 days left to get the stun gun funded.