How tracking of offenders works

A device worn on the offender's belt relays data to a monitoring centre

The satellite tracking of offenders being piloted by the government from Thursday allows their location to be pinpointed to within two metres.

Offenders wear an electronic ankle tag with a wireless connection to a belt-worn device that transmits co-ordinates to the tracking system.

An alarm is triggered if this device is separated from the anklet.

The technology will be used following an offender's release from prison or to ensure compliance with an exclusion order stopping an offender going to certain places.

Tracking levels

The 12-month trial in Greater Manchester, Hampshire and the West Midlands will track 120 persistent offenders, those guilty of domestic violence and sex offenders.

The Home Office says two types of tracking - passive and hybrid - will be tested.

Time will tell, but it could be a significant advance in how we deal with offenders James Vyvyan-Robinson Reliance Monitoring Services See how the system works

The equipment monitors and stores details of the offender's movements in real time, but with passive tracking that information is only relayed to a control centre when the device is connected to a landline telephone.

That would typically take place at the end of each day, or more frequently where there is thought to be a heightened risk.

Offenders considered the highest risk could face hybrid tracking, which would work like passive tracking unless they breached tracking conditions, such as by entering an exclusion zone.

The tracking device would then switch to active mode and transmit real-time location information to the monitoring centre.

The information is shown as location trails on a computer screen map, down to a level of detail the operators say shows which side of the street and which direction a person is moving.

'Deterrent effect'

The pilots are taking place under existing electronic monitoring contracts with suppliers Securicor, Reliance and Premier.

The electronic tagging already in operation across the UK sets off an alarm when an offender breaches a curfew, such as by leaving home after a certain time, but offers no information about where they have gone.

James Vyvyan-Robinson, operations director of Reliance Monitoring Services, which is running the Hampshire pilot, said: "What it gives is the whereabouts of an individual outside their premises.

"Where in the past we have known whether they have gone out or not, we have not known where they have gone - that is what satellite tracking will give.

Separating the tracking device and tag triggers an alarm

"It will give us the ability to let other agencies know where that individual has been and, most importantly, the ability to exclude them from certain areas.

"It gives another layer of supervision that has never been there before. It will provide additional protection to the community and a more robust way of seeing what offenders do and when they do it.

"Time will tell, but it could be a significant advance in how we deal with offenders."

A Home Office spokesman said that satellite tracking would "certainly have a deterrent effect" against repeat offending.

Cost

The government has this year set aside £3m to cover the start-up, management and evaluation of the trials.

If they are deemed a success, it plans to use satellite tracking to monitor the 5,000 most prolific offenders in England and Wales.

The Home Office says the cost of tracking individual offenders will depend on the intensiveness of the tracking and the overall number of offenders involved, but estimates it could average £68 per day.

Home Secretary David Blunkett has said satellite tracking technology could create a "prison without bars" where "first-time low-level non-violent offenders would actually be tracked rather than sent to short-term prison sentences".

Several US states use satellite technology to monitor offenders' movements.

Florida introduced the technology in 1998 and is the largest user, tracking around 3,000 criminals.

1: Offender wears tracker device on belt, with wireless connection to ankle tag.

2: Belt device tracks own location using GPS satellite signals.

3: Location data transferred from belt device to telephone network.

4: Data sent to control centre, which can be specifically alerted if offender enters exclusion zone or breaks other conditions. Radio frequency alarm also sent if tracker and ankle tag are separated.

5: Offender's position shown as location trails on computer map.

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