Detector vans are mostly a hoax. It's thought that they worked by detecting electromagnetic radiation given off by CRTs, if they worked at all. Those are obsolete, so the point is moot anyway. But how should they be able to tell apart a TV and a computer monitor? Furthermore, you can use a TV and not connect it to an antenna—Smart TVs and Chromecast/Roku/Fire TV/Apple TV/... make that a perfectly viable use case. Such use isn't subject to TV licencing in the UK, only watching live broadcasts (including streaming) is.
>only watching live broadcasts (including streaming) is.
Also using BBC iPlayer even for non-live content now requires a TV licence.
Apparently this changed in September 2016. Previously, watching non-live content didn't require a TV licence.
detector vans are a lie, especially now there are no CRT tvs. the "vans" they did use could detect the radiation coming out of the tv that matched the tv signal they were watching.