The UK’s first road signs which will electronically detect and warn drivers who are using mobile phones have been introduced. These signs can detect when signals are being transmitted by a mobile telephone inside a car, and then flashes a symbol of a mobile phone with a line through it to remind drivers not to use their handsets while behind the wheel.

The road signs work by using a scanner to detect the radio signals emitted when someone in the car is connected to a call, with this data used to illuminate a sign further down the road.

The scanner can pick up both mobile phone radio signals and Bluetooth signals, and differentiates between the two. This means those using Bluetooth for a hands-free connection, will not be warned by the sign, as if the scanner picks up a Bluetooth signal, it will disable the light.

However, they do not monitor data connections, meaning those using internet services on their phones will not be detected.

The first of three £6,000 electronic signs was yesterday introduced in Norwich, Norfolk.