A roadside system that detects if a mobile phone is in use in a passing vehicle is being piloted in a UK first.
Despite being unable to pick up whether the driver is using the phone, it is hoped it will act as a deterrent to people making calls behind the wheel.
The technology picks up the phone signal in the vehicle and activates a roadside warning sign of a mobile with a red line through it.
Being initially tested in Norfolk, the system cannot record footage.
However, the it is designed to pick up whether the phone is being used hands-free or via a vehicle's Bluetooth system and will not trigger the sign in those circumstances.
Chris Spinks, of Westcotec the firm behind it and former head of roads policing in Norfolk, said: "So many people, by force of habit, can't resist using their phone.
"It's a huge problem on our roads and drivers know there is no remote detection system.
"The system cannot differentiate between a driver and the passengers on a bus, for example, but this goes some way towards remotely warning drivers that they can be detected using their phone.
"Hopefully, as time goes on it will become as socially unacceptable as drink driving."
The signs are in place in four locations in Norfolk before being moved on to new sites within the county in a month's time.
Statistics from the devices will be shared with Norfolk Police, the county council said.
The council said that enabling the system to record specific number plates could be a "future development" with it.
Insp Jonathan Chapman, of Norfolk Roads Policing unit, said: "Any scheme which prevents this kind of behaviour is welcomed.
"Using a mobile phone at the wheel is one of the fatal four road offences which can have devastating consequences if it causes a fatal or serious collision.