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, it is designed to pick up whether the phone is being used hands-free or via a vehicle's Bluetooth system and as a result will not trigger the sign.
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.
"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."
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.
How does the system work?
Using a directional antenna, the detector picks up radio waves emitted from a phone handset, and measures the signal strength and length of activation.
When a signal is detected of a duration and signal strength sufficient to activate the system, the detector triggers the sign.
The detector is able to distinguish Bluetooth connections which, when picked up, will prevent the trigger activation.
Peter Williams, RAC road safety spokesperson, said: "While this new signage is no replacement for a uniformed police officer catching someone in the act, it could be enough to make some drivers think twice - and that has to be a positive step forward.
"So ironically, just as technology has enabled the problem of drivers using mobile phones illegally, it can also be a big part of the solution in getting people to stop."
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."
Kate Goldsmith, whose daughter Aimee was one of four people killed when a lorry driver smashed into stationary traffic while he was scrolling through music on his smartphone, said she "welcomed" the technology, but said police need video evidence to get convictions.
She said: "Law enforcement technology has been lagging behind for a decade and not made any easier by motor manufacturers that encourage users to plug in their devices before each journey.
"The tragedy of Aimee's death and trauma to my son who followed in the car behind has made the use of devices in vehicles less of a debate for me.
"When you're driving, do just that and nothing else."