The taser gun, an electroshock weapon used by police departments worldwide, is no stranger to bad press.

Last September, campus police officers at the University of Florida scuffled with Andrew Meyer, a student who had just posed a long and angry series of questions to Senator John Kerry (D-Mass.) during a forum at the school. As Meyer finished speaking, officers surrounded him and directed him out of the auditorium. Meyer yelled, resisted them, and demanded to know what he had done wrong. ”You're going to get Tased if you don't put your arms behind your back,” an officer said. Meyer continued to struggle and yelled, ”Don't Tase me, bro!” One of the officers fired his Taser Electronic Control Device, and Meyer screamed, his voice breaking.

Within hours, the video record of the event in Gainesville appeared on the Web and became an instant YouTube sensation. The American Civil Liberties Union and Amnesty International chimed in with support for Meyer, whose memorable ”Don't Tase me, bro!” cry leaped into American popular culture on T-shirts and baby bibs. Newspapers across the United States questioned whether the campus police were right to use the Taser, whether it was cruel, and whether Meyer had deliberately provoked the officers into stunning him.

The explosion of attention surrounding the incident reflects a deep public ambivalence toward the electroshock weapon and its use. Meyer's experience is but one of many high-profile cases in which the use of a Taser to subdue a recalcitrant troublemaker may not have been warranted. Last year, a student at the University of California, Los Angeles, was shocked in Powell Library, an event that generated a similar public outcry. The student, Mostafa Tabatabainejad, was using the computer lab after hours and didn't show officers his student ID card when asked to do so. His continued refusal to comply or leave the library led the campus police officers to apply Taser shocks to him repeatedly. Reports after the fact acknowledged police error—the officers had overreacted and were too ready to deploy their high-tech gadget in a situation that didn't call for violence.

The screams of people being shocked by a stun gun sound eerily similar to the blood-curdling cries of torture victims, so incidents that involve unarmed students raise hackles. But there's another factor underlying the public distrust of Tasers: the possibility that they can kill people.

In the period between 2001 and 2005, Amnesty International reported, 150 people died in the aftermath of receiving shocks from a Taser. In only a handful of the cases did medical examiners cite the shocks received as a cause of death. Even so, the considerable uncertainty surrounding the physiological effects of a Taser shock, as well as ambiguity regarding when it should be used, have bred an atmosphere of distrust and fear.The electroshock gun used by police—the Taser X26, made by Taser International of Scottsdale, Ariz.--fires barbed electrodes. A shot releases two probes, and those probes must either both make contact with their target, or one must strike the target and the other the ground, to complete the electrical circuit. The electrodes are attached by long, thin wires to a waveform generator that sends muscle-locking electric pulses into the target.

Situations where police have been able to successfully disarm suspects without causing permanent injury are the reason these weapons have gained widespread use. In an October case in the Czech Republic, for example, a kidnapped child was rescued by police who used Taser guns to immobilize her captors. According to a 2006 report by the Police Executive Research Forum, a law-enforcement policy organization in Washington, D.C., more than 8000 police and sheriffs' offices across the United States have adopted the devices, which are widely used in Canada and the United Kingdom as well [see graph, ”Don't Tase Me, Old Chap!”].Police departments in Australia, New Zealand, and France started using the devices after Taser International introduced an attachable video camera. The guns also now release bits of identifying confetti with every shot, and the time and duration of each trigger pull is recorded in the gun's memory. According to Taser, its guns are now fired more than 620 times a day and have been used a total of more than 680 000 times worldwide.

Any new technology that is designed for violent encounters should be carefully assessed. Unlike medical devices, Tasers don't have to undergo testing and receive approval by agencies such as the U.S. Food and Drug Administration, at least not in the United States. Partly in response, several local and state legislatures have considered introducing laws restricting the stun guns' adoption, and most police departments, if not all, have instituted guidelines on the proper use of Tasers.

Analyses conducted by British and Canadian police research centers and by the U.S. Air Force concluded that Tasers are generally effective and do not pose a significant health risk to the recipients of a shock. In Portland, Ore., meanwhile, police found that 25 to 30 percent of the situations in which a Taser was employed met the criteria for the use of deadly force. Other police departments have released statistics showing a decline in the number of deaths of suspects and officers in the months following the introduction of Tasers. But research by the Police Executive Research Forum has raised the concern that multiple activations of Tasers may increase the risk of death.

Even if Tasers are proven to be entirely safe, there's the bigger question of whether the stun guns encourage police brutality. A Taser shock leaves almost no visible scarring or bruising, as a clubbing or a beating typically would. Could the absence of physical scars lift a psychological restraint on officer behavior? Should every Taser gun have a built-in video camera?

Equipping law-enforcement services with Tasers is likely to reduce the number of bullets officers fire from their handguns and therefore the number of serious injuries and deaths. At the same time, it may lead police to inflict an unwarranted amount of pain on individuals who commit only minor crimes.

The broader questions regarding the social effects of stun guns are, however, beyond the scope of this discussion. The two articles that follow investigate the physiological effects of electric shock. The first is by Mark W. Kroll, an electrical engineer who has helped invent numerous electrical medical devices and who sits on the board of Taser International. The second is by Patrick Tchou, a cardiac electrophysiologist at the Cleveland Clinic, who has tested Tasers experimentally on pigs.