The recent deaths of three men in Canada after police stopped them in their tracks with TASER guns have resurrected the debate over use of the weapons, which utilize electric pulses and strong muscle contractions to incapacitate people considered to be a threat to officers and the public.

The three separate cases are still under investigation, but the association between them and the technology has led to misconceptions about the way these weapons affect the body, law enforcement and TASER International say.

TASERs, which represent the lion's share of all electronic-control devices used by law enforcement, work by shooting two metal probes that release electricity into the body, causing neuromuscular incapacitation. Generally, the victim feels as though "he is in a full-body charley horse," but does not lose consciousness, says Steven Ashley, a former deputy sheriff in Livingston County, Mich., who retired from the force in 1989 and is now a law enforcement consultant. "They short-circuit the electrical signals in the body."

The deaths in Canada, however, have some local politicians calling for a review of how the weapons are used, and some health care officials say these weapons are not nearly as benign as portrayed. A report released earlier this year by the Heart Rhythm Society, a Washington, D.C., organization of cardiac arrhythmia doctors and patients, found that electronic-control devices like the TASER may trigger "significant arrhythmias" in patients with pacemakers.

But Ashley, a senior master instructor for Scottsdale, Ariz.–based TASER International and an instructor for its competitor, Stinger Systems, Inc., in Tampa, Fla., disagrees that TASER weapons damage the heart or other internal organs. "The energy they emit follows the grain of the muscles and impacts sensory motion and the motor control," he says. "It doesn't go off searching for internal organs." The most common lingering effect after the muscle contractions, he says, is muscle fatigue lasting a few hours. But, he admits, "you don't know exactly how each individual will react." Other variables determining victims' injuries are how hard they fall and where they land.

TASERs contain two probes, each with a half-inch metal tip roughly the size of a fishhook that is designed to latch onto a target's body and / or clothes. The probes are packed into cartridges and are propelled at their target using compressed nitrogen. The probes travel at 180 feet (55 meters) per second when fired, spread one foot (30 centimeters) apart for every seven feet (2.1 meters) they travel and must land at least four inches (10 centimeters) from one another on the intended target to complete the circuit and channel an electric pulse into his or her body. If the probes are less than four inches apart, the TASER will deliver a shock, but not incapacitate the person.

A TASER uses up to 50,000 volts of arcing voltage to deliver a charge via the tips of its probes. Ashley, however, says TASERs are typically programmed to fire for five seconds, not enough time for a full discharge—the cycle can be stopped in less than five seconds if the weapon's safety lever is moved into the "safe" position. The high voltage is available so that a TASER's charge can reach across a gap of about two inches (or five centimeters) of air or clothing to connect with the victim's body; the probes do not have to actually penetrate skin to work. When fired, the TASER X26 weapon, a model commonly used by law enforcement, operates at 19 pulses per second at a pulse duration of 100 microseconds to deliver an average current of 2.1 milliamps. (Editor's note: in an earlier version of this story, it was mistakenly reported that a TASER has a peak current of 3 amps.) Put in perspective, a University of Illinois at Urbana-Champaign study indicates that at 20 milliamps, breathing becomes labored. At 100 milliamps, ventricular fibrillation of the heart—an uncoordinated twitching of the walls of the heart's ventricle—occurs.

"The TASER is the only weapon the police have that doesn't rely on pain compliance," Ashley says. Batons, beanbag rounds and rubber bullets can be used as nonlethal law enforcement tools, but they are only effective if a suspect ultimately surrenders. Although such weapons are often referred to as "less lethal," Ashley disagrees with this characterization. "Nothing is risk-free," he says, adding, "A TASER is not less lethal, it's nonlethal."

There are hitches. For instance, TASERs will not work properly in situations where the probes get caught in a target's clothing too far from the body to deliver a jolt, only one probe makes contact or the wires connecting the probes to the gun are damaged. "We need that tool that will absolutely incapacitate someone for 10–to–15 seconds without longterm effect," Ashley says. "TASER gets us closer to that than any other weapon has."

An investigation into the mid-October death of Robert Dziekanski, 40, at Vancouver International Airport after Royal Canadian Mounted Police used a TASER to subdue him will either confirm or contradict Ashley's view. Investigations are also underway into the deaths a month later of Robert Knipstrom, 36, in Chilliwack, British Columbia, and Howard Hyde, 45, in Dartmouth, Nova Scotia, after they were TASERed.

The technology on which current TASER weaponry is based was created in the 1970s by physicist John H. "Jack" Cover, a former director of science and engineering for the space division of aircraft maker North American Aviation (which Boeing bought in 1996). Cover's invention, however, required the use of gunpowder to discharge its probes and was considered a firearm. Cover named his invention "TASER" after a fictional weapon in Victor Appleton's 1911 adventure book Tom Swift and His Electric Rifle.

TASER International's first widely used product—the AIR TASER Model 34000, which ran on a nine-volt battery—hit the market in late 1994. When the trigger on the 34000 was pressed, it would administer a charge for 30 seconds during which the shooter could place the device on the ground and get a safe distance away from the person receiving the jolt, says Steve Tuttle, the company's vice president of communications.

For the Advanced TASER M26 that debuted in 1999, the company tweaked the number of pulses per second and their duration in order to achieve a higher level of muscle incapacitation. The goal was to do a better job of stopping individuals aggressive enough to overcome the previous model's charge, which Tuttle says stopped 84 percent of people. The M26, which ran on eight AA batteries, also recorded the time and date each time it was fired as a means of curbing misuse.

The X26 followed in 2003 and was 60 percent lighter and smaller than its predecessor, in part because it ran on two lithium ion camera batteries. In addition to having two LED lights to illuminate a target, the X26 also featured a new waveform that, Tuttle says, more efficiently delivered a shock to the body. Whereas the range of earlier TASERs was 15 feet (4.6 meters), the X26's probes could travel as far as 35 feet (10.5 meters).

The next generation TASER—the eXtended Range Electronic Projectile (XREP)—is being designed to fire wireless probes as far as 65 feet (20 meters) from a half-ounce (14-gram) cartridge that fits into any standard 12-gauge shotgun. TASER plans to start training instructors in the XREP's use by the middle of next year. Another new weapon under development is the Shockwave, which Tuttle refers to as "an area-denial system" that simultaneously fires six TASER cartridges up to 25 feet. Scheduled for availability late next year, the Shockwave is designed to be used by military and Homeland Security personnel at airports, checkpoints and other open spaces.

The company expects it will need to weather a storm of scrutiny in Canada in the coming months similar to what it experienced in 2005, when the U.S. Securities and Exchange Commission launched an informal inquiry after reports questioned the weapon's safety. That inquiry was dropped the following year.