TV Licensing, which runs the system for the BBC, said it hoped the threat of the new technology would encourage the estimated 1.8 million licence evaders to buy a pounds 97.50 colour licence in the run-up to the Christmas viewing boom.
The equipment is the result of three years' research. It can detect a switched on television whether it is receiving cable, terrestrial or satellite programmes and weighs only one-tenth of earlier models, making it easier to sweep high-rise blocks, for example.
TV Licensing said it was likely to catch more dodgers than the 200,000 snared over the past six months. The maximum fine for evasion is pounds 1,000.
Detector vans have also been fitted with new portable computers to check with a central database whether a householder has a licence.
TV Licensing said about 1,000 evaders were caught each day by its 400 officers even though at the end of September there were a record 22 million licence holders.
Simon Ablitt, director of field operations for the organisation, said: "This new equipment will be quicker and easier and more effective. If people don't heed the warnings, the number we catch will go up."