Lone workers at Guy's and St Thomas' foundation trust are using a new security device that allows them to communicate discreetly with a back-up call centre in potentially hazardous situations.

The trust is one of a few hospitals in the country and the only one in London using the device, which is disguised as an identity card holder.

Guy's and St Thomas' 80 community midwives feel the greatest benefit from the system, which has been implemented by community and postnatal lead midwife Mitra Bakhtiari.

Clinical director of women's services at Guy's and St Thomas' Marie McDonald said: "As one of the biggest maternity units in the country, keeping our midwives safe is a top priority for the trust.

"Home visits are an important part of their work and in the majority of cases they are lone workers. Identicom has enhanced the safety of our 80 community midwives visiting patients at home."

Mitra said it is important that the trust is able to provide care to those who need it, particularly for those who have difficulty accessing services, high-risk groups or those who live in unsafe areas.

But she added: "We must also take responsibility for the safety of lone workers. It is important that we proactively protect our midwives so they can carry out their job in the safest possible environment."

Various devices were trialled in 22 trusts following the NHS report Not Alone - a guide for the better protection of lone workers in the NHS in 2005.

The system selected by Guy's and St Thomas' connects the user with a call centre. If they believe they are entering a hazardous situation, they press an amber alert button, providing important location information to a monitoring centre.

If the red alert is then pressed, the centre's support staff can listen in to what is happening and make an assessment as to the level of support required, involving the police if necessary. The operator also verifies the user's location through the amber alert and location positioning technology. In the event of a verbal confrontation, the centre can also record the conversation for future action.