One afternoon in May, Al Jazeera accompanied police sergeant Joseph Paul on patrol in San Jose, California, a city of just under a million people. As Paul wheeled his cruiser down the highways and streets of his city, he said his daily routine is full of  potential dangers.
“On patrol you have absolutely no idea who you're dealing with, what their story is, why they're where they are, why they're doing what they're doing,” Paul said.  “So you have to always be alert.”
On this particular patrol, Sgnt Paul did not encounter any dangerous situations. But the conditions of police work - the unpredictability, and the way that even a routine traffic stop can suddenly turn violent, are what police departments around the US often cite in support of arming officers with Tasers. In 2004, the San Jose department  became one of the first law enforcement agencies to equip each of its patrol officers with a Taser.
The Taser is a battery-operated device shaped roughly like a pistol. When fired, it expels darts trailed by thin wires. When the darts hit a person's flesh, tens of thousands of volts of electricity begin coursing through the person's body. The Taser can also be pressed directly onto a person and activated by a trigger.
When hit with a Taser, people suffer excruciating pain, often lost control of their muscles, and fall to the ground in temporary paralysis.
Tasers are supposed to be a non-lethal alternative to police use of firearms. But sometimes, people who are tasered die. Over the past dozen years or so the death toll has risen alarmingly.
In San Jose, six people have died after being tasered by police - one of the highest number of fatalities of any city in the country.
In May of 2008, Steven Salinas was drunk, naked and holed up in Room 119 of a cheap hotel called the Vagabond Inn. Salinas, who was unarmed, had committed no apparent crime when San Jose police burst in, clubbing and tasering him repeatedly. Salinas died of cardiac arrest.
Unarmed 20-year-old student Phoung Ho did not die after being tasered and clubbed by police as he lay handcuffed on the floor of his home.  But the city was forced to pay him an undisclosed sum after Phuong took it to court.
I spoke to Rina Chakraborty, Western regional director of Amnesty International, about a study her organisation recently completed.
“Our concern with Tasers are that they are  unsafe, unregulated and prone to use and abuse,”  Chakraborty said. “What we have found is that since 2001, at least 500 individuals in the US have died after being shocked with Tasers by police either while being arrested or in jails.”
Amnesty is particularly concerned by the inappropriate use of Tasers by police against people who are unarmed, not acting aggressively,  and may in fact have committed no crime.
“We are finding Tasers are being used when there has been no serious threat posed to police,” Chakraborty said. “We found cases where an 82-year-old woman has been shocked with a Taser for waving around a hammer, or cases where schoolchildren as young as 10 or 11 are being shocked with Tasers by police.”
What Amnesty International has found is that in 90 per cent of the cases investigated, individuals were unarmed.
In many cases, people who die after being shot with Tasers have underlying medical conditions such as irregular heart rhythms. A large number of people who are shot with Tasers are mentally ill, developmentally impaired, drunk or on drugs.
Amnesty calls for strict national guidelines on Taser use, and better training of police officers, to prevent more deaths.
San Jose Police Department spokesman Sergeant Jason Dwyer said Tasers are simply a useful tool for police.
“A taser gives us another option that we can use,” Dwyer said. “If you give officers a tool like a Taser, one more tool in their tool box so that they can use something that's less than lethal force, you may save both the officer's life and the suspect's life.
Dwyer admitted that “sometimes a suspect will expire after the use of a Taser”. But he said it is always up to prosecutors and police supervisors to decide whether officers acted without justification or used excessive force. Dwyer said that so far, no San Jose police officer has been disciplined for using his or her Taser in an unauthorised manner.