Using the latest technology the unit is able to identify what type of signal is being transmitted or received by the handset and whether it is being used via the vehicle's Bluetooth system.
The sign's introduction comes amid increasing concern about the risks posed by using a phone while driving.
The first sign which detects if drivers are using a mobile phone whilst driving and then flash up a warning has been installed in Norfolk.
"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". It won't be able to record registration numbers for the cars or issue fines, but it will still serve in future crackdowns by the police.
Mr Spinks said: 'The aim of the technology is to remind drivers of the law and to get off their phones'.
Westcotec also says it can't differentiate between legal calls made by passengers and when it's the driver being a baddie, which is presumably why an advisory road sign is all it offers.
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 past year.
These signs can detect when signals are being transmitted by a mobile telephone inside a auto, 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.
Using a mobile phone at the wheel now carries a punishment of six penalty points and a £200 fine, which was increased from three penalty points and a £100 fine past year.
If it proves successful in Norfolk, the phone-detecting road signs may be rolled out across the country.
The system will initially be used at sites in Attleborough, Holt, Norwich and Toftwood. Norfolk County Council road safety team will be working closely with the roads policing team to share statistics provided by the detection system.