Stun Guns use high voltage and low amperage to temporarily disable an attacker. They disrupt voluntary muscle movements and cause a great deal of pain, leaving enough time for you to get away from a dangerous situation. Most law enforcement organizations make stun guns available to front line officers because of their proven effectiveness.
Let's go over the above statements in detail. First of all, like most weapons a stun gun isn't a "magic wand" and it isn't "setting phasers on stun." Stun guns are trusted because they work on age-old electrical principles. A stun gun (including a TASER's twin projectiles and the prods on a stun baton) has two contact points that deliver the electricity. Many models have a test mode that lets you run a small arc of electricity between the contacts. When that shock moves through human flesh . . . that flesh's owner doesn't like it very much.
Despite the name, most stun guns are actually close range weapons. You must touch your attacker with the weapon's contacts. TASERs are the exception, since their contacts are twin darts that are shot out, trailing a wire to deliver the electrical discharge. The weapon's exact effects depend on its wattage, amperage and the length of time the contacts touch your attacker. A fraction of a second's contact will cause pain and muscle contractions. Two or three seconds is often enough contact time to make an attacker drop to the ground. Past that, the shock might incapacitate the assailant for longer.
The importance of contact time is why Taser International recommends that TASER civilian model users abandon the weapon and run after use (Taser International will replace it if they get a police report about the incident), but their stun guns use projectiles that will stay in the target unless forcibly removed, and deliver the shock even after being abandoned, for a maximum of five seconds.
Remember: Electricity is dangerous! A stun gun isn't as dangerous to the target as a firearm but it can still cause long-term health complications. You shouldn't worry about that when someone's threatening you, of course, but like all weapons, a stun gun isn't a toy and should be used carefully. Make sure you keep it safe, secure and out of reach of your children, but practice drawing it quickly in case you need to use it. Make sure it's fully charged at all times. Finally, be aware of local laws. See our Stun Gun Laws page for legal information.