They were the sinister-looking white vans that had generations of Glasgow locals glued to their windows instead of their TV sets.
But some reckon the UK's analogue age TV detector vans were little more than an elaborate hoax to scare us into paying our licence fees.
If you're of a certain age, you'll remember well the palpable fear that washed over your street as a friend or family member announced that the telly detector van was in the area.
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The arrival of the white vans, which were emblazoned with 'TV Licensing' in blue lettering along the sides with an elaborate array of antennae on their roofs, would prompt terrified mums, dads, aunties and uncles to pick up their phonebooks and dial the number of everyone they knew to warn them to switch off their tellys.
Of course, as long as you were paying your television licence fee then you had absolutely nothing to fear.
The vans made their debut in the 1950s, and, to take a line from Billy Connolly, they were "about as welcome as a fart in a spacesuit" as far as the British public were concerned.
The mobile units worked by detecting the electro-magnetic field emitted by traditional cathode ray tube television sets that most people owned up until the 2000s.
And according to BBC-funded public service information ads, they could pinpoint non-licence payers with devastating accuracy.
In one such TV advert, understood to have been broadcast in the 1970s, a supposed licensing official declares: "Yes, there's a TV set on at number 5. It's in the front room and they're watching Columbo".
Detector vans used antenna pairs that could identify non-payers quite easily. As vehicles passed by a television set-owning property, the signal strength intensified and van operators would be able to determine which side of the street the signal was coming from. The placement of an individual's TV antenna was largely irrelevant.
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During the 1970s, the number of Brits forking out for their annual TV licence hovered at between 15-18 million people from an overall adult working population of around 40 million. In other words, while many will have shared the same household, the authorities weren't daft.
But while millions of us clearly weren't taking any chances and dutifully coughed up the cash, there were many out there who remained sceptical of the TV detector vans - some even reckon they were all for show.
On a recent post on a popular nostalgia group on Facebook, locals recalled seeing the dreaded vehicles prowling their streets. Naturally, rumours were abound that they were only to scare us into paying the licence.
One member said: "A Freedom of Information request confirmed that not a single prosecution ever took place using a TV Detector Van as evidence….mainly for show."
"I swear they were a scam just intended to scare people into paying!" another local wrote.
Another local commented: "Remember one that drove into Broomhouse circa 1963 and was pelted with all sorts stuff. Made a quick exit, and never returned!"
Another added: "Apparently these vans were just a ploy, they couldn't detect an unlicensed tv if you set fire to it and stuck it in the garden. There was a person sitting in the back turning a handle to move the aerial things on top of the van to make it look good."
Whether or not they actually worked as well as the likes of the BBC claimed is still up for debate in the eyes of many, but there may be some truth in the notion that TV detector vans were simply used a scare tactic.
In 2013, the Radio Times managed to obtain a leaked BBC document that made no mention of TV detector vans being used to catch non-payers of the licence fee.
Subsequently, it was revealed via a freedom of information request that data from TV detector vans has never once been used in court to prosecute a TV licence non-payer.
Responding to hoax speculation, a BBC official remained coy about how the vans were used, stating: "Detector vans are an important part of our enforcement of the licence fee.
"We don't go into detail about how many there are or how they work as this information might be useful to people trying to evade the fee."
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