The Yellow Jacket is a case for the iPhone 4 and 4S that doubles as a 650,000-volt stun gun to ward off the dangers of society. They are currently running a campaign on for funding and have a myriad of options for the early investors; they normally retail for $125, but you can get the Early Bird special for $85, your choice of color (currently black, white, or pink).
The idea behind the product is to put a defense tool on something that you already have on you at all times.
An iPhone Case Doubles as a Stun Gun | PCWorld