It's strange the things you can end up researching for a book. The next Darkeninstone book Outcast has some elements of a thriller, hence the need for accurate info on Tasers. This wasn't my only source but it gives an overview.
More than 225,000 officers and 120,000 U.S. citizens carry Tasers, according to a 2011 report by the University of California, San Diego, Medical Center and San Diego State University. Tasers are used by law enforcement in all 50 states as a less lethal alternative to handguns. They can be fired from 20 feet away to incapacitate an assailant, while stun guns require contact with clothing or skin to inflict pain. Despite favorable outcomes relative to handguns, Tasers still do cause bodily harm, including barbed dart injuries and trauma from falls.
The Taser device releases a pair of 9-millimeter barbs, attached to the gun by thin copper wires, to deliver an electrical pulse that causes involuntary muscular contractions. The effect has been described as a full-body “charley horse.” People seen in emergency departments afterward for removal of the barbs usually report pain, muscle aches and anxiety. In addition, there is a risk that barbs may strike vulnerable areas such as the eyes or genitals.
If you want more, here's a video:
So if you needed a reason to be a good boy or girl from now on, there you go. Have you ever researched something that seemed strange?