Abstract: A personal defense device may attach to a mobile electronic device, such as a mobile phone, smart phone, blackberry, mp3 player, iPod® or the like. The defense device may interact with the mobile electronic device and would include one or more deterrent, such as a chemical deterrent, sound, light, electrical or projectile which would be emitted from the device. Since personal defense devices are only effective when people have them close at hand, most mobile phone users keep their phone readily available. Thus, a personal defense device, attached to their mobile phone, would also be readily available.