British road safety authorities are reportedly testing a roadside system for detecting phone use in cars.
The road signs work by using a scanner to detect the radio signals emitted when someone in the auto is connected to a call, with this data used to illuminate a sign further down the road.
The sign, which for the next four weeks will be at Holt Road, Norwich, is able to identify what type of signal is being transmitted or received by the handset and whether it is being used via the vehicle's Bluetooth system.
The first of three £6,000 electronic signs was yesterday introduced in Norwich, Norfolk.
Although the signs can not tell whether a driver or passenger is using a handset it is hope they will help remind people of the dangers of using phones while driving.
The system, which can tell the difference between active phone calls and other activities based on the strength of a signal and how long it lasts, flashes up a red warning signal to drivers when it detects a call.
The signs have been set up in four locations around Norfolk and will be moved to new sites in a month.
Norfolk County Council's road safety team have worked with speed and warning sign specialists Westcotec on deploying the next-level signs, which are a first for United Kingdom roads.
This scheme is a good example of how we can work with local authorities to make using a mobile phone whilst driving as socially unacceptable as drink or drug-driving.
Insp Jonathan Chapman, of Norfolk Roads Policing unit, said: "Any scheme which prevents this kind of behaviour is welcomed".
Margaret Dewsbury, chairman of Norfolk County Council's communities committee, said: "Using a mobile phone whilst driving is an enormous distraction and apart from being illegal puts the lives of the driver, passengers and pedestrians at risk".
New roadside technology is being introduced to deter motorists from using mobile phones at the wheel, it will be announced today.
Iain Temperton, team manager for road safety at the county council, described the technology as "cutting-edge" and said it would be used an "educational tool" throughout Norfolk to tackle the problem.