A 340 lb. man in Miami resisted arrest, but 50,000 volts of electricity from a Taser (search) gun adjusted his attitude.

The $800 guns are changing the way police conduct business. Before introducing Taser guns, Miami police averaged 20 shootings a year, killing two to three people. In the past 19 months, they have not fired a single shot, officials with the Miami-Dade Police Department (search) said.

"That has never happened in the history of American police," said Police Chief John Timoney. "Not even a single bullet that was shot at an individual and missed — not a single bullet was shot."

Taser guns fire two pronged barbs that attach to a person's skin or clothing. The electric shock disrupts communication between the brain and the nerves, so the muscles collapse.

Four thousand police departments now use Taser guns and after more than 70,000 zaps, the weapon has never been cited as a cause of death. But Amnesty International (search) has called for a ban, saying the weapons are too easy to abuse.

"Unlike guns, unlike batons, there are very few if any traces left after the use of these weapons and so officers and those who are using them can get away with using them inappropriately without it being easily detected," said William Schulz, executive director of Amnesty International.

Go to the video box above to watch a report by FOX News' Steve Harrigan.