The first road sign in the UK that electronically identifies and gives a warning to drivers using mobile phones was introduced last week. The sign detects signals sent by mobile devices inside a car and flashes a representation of a mobile phone with a diagonal line across it to warn people that they cannot use mobile phones while driving.

The road sign incorporates a scanner that detects the radio transmissions when a car’s occupant is engaged in a call and uses this information to light a warning sign farther along the road.

The scanner can detect both Bluetooth signals and radio signals from mobile phones and distinguish between these types of signals. Therefore, drivers who are using Bluetooth to operate their mobile phone hands-free will not cause the warning sign to flash.

The scanner cannot detect data connections, so drivers using their mobile phones for Internet access will not trigger the warning signs.

The first of three proposed electronic warning signs is operating in Norwich, Norfolk. The cost of each sign is £6,000.

Authorities hope that the signs will serve as a deterrent to driving while using a mobile phone, as the signs are not capable of reading a car’s registration information and issuing a fine. Also, the sign does not have the capability to determine whether a passenger or the driver is using a mobile phone.

However, the signs will transmit the data that they collect to Norfolk police, who can use it to decide on locations for future enforcement efforts.

Drivers caught by police while using their mobile phones are subject to a £200 fine and a six-point penalty on their driver’s licence.