From the 1 September people watching the BBC using its iPlayer catch-up site will need to have a TV licence. The BBC's vans will be looking to find those who are dodging the £145.50 licence fee.
In a report from the National Audit Office (NAO), Sir Amyas Morse, NAO comptroller and auditor general, wrote: "Detection vans can identify viewing on a non-TV device in the same way that they can detect viewing on a television set.
"BBC staff were able to demonstrate this to my staff in controlled conditions sufficient for us to be confident that they could detect viewing on a range of non-TV devices."
A BBC source said: "While we'd never get into the details of how detection works for obvious reasons, the Telegraph story is littered with inaccuracies and speculation, as for example, it is wrong to suggest that our technology involves capturing data from private Wi-Fi networks."
The BBC was empowered by law to carry out surveillance of those avoiding the licence fee by the Regulation of Investigatory Powers Act (RIPA), passed in 2000.
The act has been controversial. As BBC Bitesize explains: "There are a number of people who regard the RIPA regulations as excessive and a threat to privacy and civil liberties in the UK."
However, the BBC has said it will not be able to snoop on the internet history of viewers, and it has also said it will not be digging into its record of computers than have gone onto the iPlayer website to find fee dodgers.