But some phone users may get through, as the scanners won't pick up data connections from drivers using internet service on their phones.
The road signs work by using a scanner to detect the radio signals emitted when someone in the vehicle is connected to a call, with this data used to illuminate a sign further down the road.
New roadside technology is being introduced to deter motorists from using mobile phones at the wheel, it will be announced today.
However, the it is created 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.
The first of three £6,000 electronic signs was yesterday introduced in Norwich, Norfolk.
The technology can not log number plates or be used to catch offenders yet, but these advancements are being considered for the future and it is hoped the current system will act as a deterrent.
Those caught using their mobile phones at the wheel by the police face a £200 fine and six points on their licence, following the introduction of tougher laws a year ago.
"Hopefully, as time goes on it will become as socially unacceptable as drink driving".
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The signs have been set up in four locations around Norfolk and will be moved to new sites in a month.
"We will be using the information provided by Norfolk County Council's road safety team to help us target drivers in the future but the message is simple - leave your phone alone whilst you're behind the wheel", he said.
The council said that enabling the system to record specific number plates could be a "future development" with it.
"Any scheme which prevents this kind of behaviour is welcomed".
"Using a 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".
For now, a counter will keep track of phone usage on the road to help authorities understand driver habits.
"Whilst this is still not a flawless science, the new generation of sign is significantly more accurate and reliable than the first".