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1 August 2011, 15:29 | Updated: 1 August 2011, 15:40
Royston is believed to be the first town in the country to be surrounded by cameras that track every vehicle going in and out.
The seven Automatic Number Plate Recognition (ANPR) cameras have been installed by Hertfordshire Police.
Police say the scheme is "supported by the local community".
The idea is that ANPR is a crime-prevention tool and deterrent to travelling criminals.
When a car passes an ANPR camera, its details are checked against a national database that checks for things like valid insurance and a current MOT certificate.
The system will also check for cars reported missing or stolen, and those vehicles Police suspect have been involved in crime.
Assistant Chief Constable of Hertfordshire Police, Alison Roome-Gifford said: "The law-abiding citizen has nothing to worry about.
The new system will help us to be discerning and more targeted about the cars we stop.
It helps us prevent crime, detect crime and find vulnerable and missing people."
However, privacy campaign group Big Brother Watch is criticising the scheme.
The group says the system is "intrusive" and "invades peoples privacy", and has written a letter of objection to the Government Information Commissioner.