As Tasers are made available to more police officers in England and Wales, BBC News looks at the use of the electric stun guns - seen as a "less lethal" alternative to conventional weapons.
Q: How do Tasers work?
The air Taser gun looks like a pistol but uses compressed air to fire two darts that trail electric cable back to the handset.
When the darts strike, a five-second 50,000-volt charge is released down the cable, causing the suspect's muscles to contract uncontrollably.
Electrical signals - Taser waves or T-Waves - overpower the body's normal electrical signals, temporarily confusing the nervous system.
A laser helps target the suspect and the Taser, which runs off eight batteries, works at ranges up to 21ft (6.4m).
Q: When were Tasers first introduced in England and Wales?
A 12-month trial began in April 2003 which saw specialist firearms officers in five police forces - Lincolnshire, Metropolitan, Northamptonshire, North Wales and Thames Valley - carrying stun guns for the first time.
They were only allowed to use them in circumstances where they were authorised to draw weapons.
During the trial, Tasers were deployed in 60 incidents and aimed in 40 of these incidents, but were only actually fired 13 times.
The Association of Chief Police Officers (Acpo) said: "One of the most striking findings of the trial was the deterrent effect of the weapon."
Q: How has the use of Tasers expanded since their introduction?
More than 3,000 Tasers have been issued to firearms officers in Britain since 2003.
Between then and July 2007, they were used in more than 800 incidents.
Officers could only use them when confronted by an armed attacker, but in July 2007 those powers were extended to include incidents of serious violence or threat.
From September 2007, the use of Tasers will no longer be limited to firearms officers.
As part of a 12-month trial, other frontline police from 10 forces in England and Wales will carry the stun guns.
The Home Office says these officers will undergo a rigorous selection procedure and will have to complete Acpo-approved training.
The forces taking part are Avon and Somerset, Devon and Cornwall, Gwent, Lincolnshire, Merseyside, Metropolitan, Northamptonshire, Northumbria, North Wales and West Yorkshire.
Q: How safe are Tasers?
There is some controversy surrounding the use of these 50,000-volt stun guns.
Amnesty International says the weapons, which temporarily disable a suspect, have been linked to more than 70 deaths in America.
It warns they cause "intolerable pain" and may exacerbate the risk of heart failure in people under the influence of drugs or with some health problems.
In 2006, Brian Loan, 47, died several days after being shot by a Taser in County Durham.
A coroner recorded a verdict of death by natural causes, attributing his death to heart disease, but his sister, Barbara Hodgson, refused to accept the Taser was not to blame and said future cases would prove her right.
But Tasers have become standard police equipment in the UK and are regarded as a less dangerous alternative to guns.
The Defence Scientific Advisory Council's sub-committee on the Medical Implications of Less Lethal Weapons (DOMILL), an independent group of medical experts, has issued four statements on the medical implications of the use of the Taser.
Its view is that the risk of death from primary injury with a Taser is low and certainly very much lower than that from conventional firearms.
Q: What checks are there on the use of Tasers?
During the first pilot of Tasers in 2003, all incidents in which they were discharged were referred to the Independent Police Complaints Commission (IPCC), which investigates police complaints.
Now, only if there is a complaint, death or serious injury are incidents referred.
The IPCC says Tasers are a useful alternative to lethal weapons where used appropriately.
The Home Office says it monitors and produces a detailed report every time a Taser is deployed.
This information is collated every three months and assessed by the medical panel, DOMMILL.
Every time the Taser is fired it releases up to 40 confetti-like ID tags which identify which officer used the weapon.
The weapons also have a microchip carrying data about when they were used and for how long which can be downloaded onto a computer.