The fatal police shooting of Rayshard Brooks, a black man who was found asleep in a car in a drive-through at a Wendy’s on Friday night in Atlanta, has reignited the debate over Tasers.

Mr. Brooks, 27, had fled from the police after failing a sobriety test, and grabbed a Taser from an officer during a struggle, the authorities said.

“During the chase, Mr. Brooks turned and pointed the Taser at the officer,” the authorities said, adding that “the officer fired his weapon, striking Brooks.”

Kalfani N. Turè, an assistant professor of criminal justice at Quinnipiac University in Connecticut, said the shooting of Mr. Brooks was what was known in police circles as “lawful but awful.”

That is, he said, officers are trained that they have the right to escalate their use of force if they believe someone is threatening to incapacitate them.

In the case of Mr. Brooks, Professor Turè said, other options were available to the officers: Identify Mr. Brooks through his car and track him down later, for instance, or call for backup to help apprehend him.

The episode has put a spotlight on a number of police tactics, including the use of Tasers. Here are some answers about the devices.

What is a Taser?

The devices, which have been used by law enforcement for decades, can temporarily immobilize a person — think of someone who is combative or resisting arrest, for instance — by jolting them with 50,000 volts of electricity.

A discharge, also known as a “cycle,” can last five seconds. The shock can cause pain that has been described as excruciating.

As Dennis J. Kenney, a professor at John Jay College of Criminal Justice in Manhattan, put it, “Your muscles freeze up, and down you go.”

The makers of the Taser came up with the product name as an acronym loosely derived from a 1911 book, “Tom Swift and His Electric Rifle,” Professor Kenney said.

How do they work?

The device can be used from a distance or in “drive mode,” in which the charge is driven directly into a person’s body at close range, said Robert J. Louden, a professor emeritus of criminal justice and homeland security at Georgian Court University in New Jersey.

When a Taser is fired from a distance, prongs or darts connected by wires are discharged at a person. In those cases, Tasers have a reliable range of about 10 feet, Professor Kenney said, but beyond that, their effectiveness in hitting a target becomes spotty.

Are they deadly?

At least 500 people in the United States have died since 2001 after being shocked with the devices during an arrest or while in jail, according to a 2012 statement by Amnesty International, which supports stricter limits on the use of Tasers.

The largest number of Taser-related deaths were in California (92), Florida (65) and Texas (37).

“Even if deaths directly from Taser shocks are relatively rare, adverse effects can happen very quickly, without warning, and are impossible to reverse,” Kristina Roth, senior program officer for criminal justice programs at Amnesty International USA, said on Sunday.

The shock delivered to the chest by a Taser can lead to cardiac arrest and sudden death, according to a 2012 study in the journal Circulation.

The study looked at the records of eight people who went into cardiac arrest after they received shocks from a Taser X26 from a distance. Seven of the people died.

The maker of Tasers, Axon Enterprise, formerly known as Taser International, said in a statement on Sunday that “any loss of life is a tragedy regardless of the circumstance, which is why we remain committed to developing technology and training to protect both officers and the community.”

Why were they developed?

Tasers were marketed as a “panacea,” one that would help officers deal with noncompliant individuals, said Professor Turè, who previously served in three law enforcement agencies in Georgia, including the State Police.

Tasers are a class of “less than lethal” tools designed to improve what Professor Kenney said were the “midrange options” for officers. Before Tasers, officers’ options were at the extremes — relying on verbal commands or the use of deadly force with a firearm.

Another approach, such as hand-to-hand combat, is a “perishable skill” that requires constant training, he said. “What are my options?” he said. “I would roll around on the ground with you: I’m going to lose as many of those as I’m going to win.”

Are they effective?

Axon says the devices save lives and prevent injuries.

“Our mission is to protect life and we prioritize safety above all else,” the company said in its statement. “Taser weapons are not risk free but they are proven safer than batons, fists, take downs, tackles and impact munitions.’’

The company, which said it had sold approximately 700,000 Tasers to “public safety professionals” worldwide, estimated that more than 234,000 people had been saved from death or serious injury because “an officer used a Taser device to de-escalate the situation.”

Do they de-escalate confrontations?

The devices can bring an abrupt halt to a confrontation and disable an uncooperative person, but if they are discharged and don’t work — or even when they do — sometimes the effect can be to make things worse.

If a person is angry, under the influence of alcohol or drugs, or has a mental illness, the use of a Taser can exacerbate those conditions and inflame a situation, said Joel Feinman, the chief public defender in Pima County in Arizona.

“When you look at who these things are being deployed against, this is a tool of escalation, not de-escalation,” Mr. Feinman said. “Now the police officer is thinking: ‘Now that didn’t work. Now I have to use the other tool attached to my belt, which is a 9-millimeter handgun.’”

Police agencies in major cities have rated Tasers less than effective, according to “When Tasers Fail,” an investigation by American Public Media last year.

The site looked at 3,000 fatal police shootings between 2015 and 2017 that involved the use of a Taser and found that in 258 of the cases, a Taser “had failed to subdue someone before the police shot and killed them.”

In addition, in more than a third of the cases, the person became more aggressive after the device was used, which may have contributed to an escalation of the incident.

What else can go wrong?

Professor Louden said a person’s physical stature — height and weight — and how amped up they might be on adrenaline can play a role in being resistant to the effects of less-than-lethal methods.

Professor Louden, a former hostage negotiator for the New York Police Department, recalled once trying to deal with a barricaded person with a mental illness who had a machete taped to his hand. Officers used mace, he said. “He took I don’t know how many canisters to the face, and it had no effect,” he recalled.

In the case of someone who is high on a mind-altering drug like PCP, also known as angel dust, Tasers are ineffective. “They walk right through it,” Professor Turè said.

Problems also surface even when the prongs successfully latch onto a person.

Tasers are most effective when connecting to light clothing but are less so with heavy winter gear, like a leather coat. Sometimes, only one prong will attach, and sometimes the devices are not properly charged, experts said.

Are there reforms being considered?

Part of the underlying problem is that the police culture does not emphasize methods to defuse situations, Professor Turè said. He said that in his 200 hours of training to become a police officer, 192 hours were dedicated to the use of force and only eight to de-escalation.

Police departments have their own policies and practices for when Tasers should be deployed, he said, and there is no reliable universal data tracking their use.

“Despite the choppy evidence of their effectiveness,” he said, “you have 18,000 police departments not really in any conversations with each other.”