The device is intended to help staff who visit patients' homes alone

Staff in England will be able to use the Identicom device, which looks like a normal ID card holder but is fitted with the latest mobile technology.

If they find themselves in a potentially dangerous situation, they can secretly activate the alarm which connects them to a 24-hour call centre.

The worker's location can then be identified, and police can attend.

NHS staff said they felt safer and more at ease in their working environment when using this device Jim Gee, NHS Security Management Service

The device also allows a phone line to be opened so sound from a violent incident is recorded and could be used in any legal action.

A hundred NHS staff have already tested out the device successfully.

The Department of Health has also published advice on how staff working alone in the community can be protected, including ensuring all those in that situation are trained to deal with potentially violent situations.

There were 116,000 incidents of physical and verbal abuse in the NHS in 2002/2003.

Court evidence

Announcing the decision to make the device available, the Health Secretary John Reid said: "I am determined to do everything within my power to stop NHS staff suffering from violence and abuse.

"They dedicate their lives to caring for the sick and in return they deserve respect.

"Anybody who attacks our staff will face tough action and the possibility of jail.

"Up to 100,000 staff work alone in the NHS everyday and thanks to this device they will have the knowledge that help is only a button away."

He added: "As recordings of incidents can be used as evidence in court hearings, it also offers the police and the NHS Security Management Service valuable information in punishing these criminals."

Jim Gee, chief executive of the management service, said the trials of the Identicom device had been successful.

"NHS staff said they felt safer and more at ease in their working environment when using this device and I hope that NHS organisations take advantage of the opportunities which are now presented to properly protect lone workers."

Health visitor Anne Lewis, who has been testing out the device in North Liverpool Primary Care Trust, said: "I visit up to 10 families a day and although problems are rare you never know what you might encounter.

"The device is easy to use, it records my whereabouts each time I walk up to a house for an appointment meaning that I can always be tracked down.

"It is also very discreet; it doesn't look like a panic alarm which means that I can secretly activate the alarm without arousing the suspicion of the patient and potentially inflaming the situation."