Scare tactics definitely play a part of it but, having seen official documentation covering up to reasonably recently (can say no more, sorry), I can confirm the technology described did exist, continued to evolve beyond that, detection was possible, and the vans were / are real. I’m sure it’s continued to evolve since those old docs too, and I can’t say it was ever particularly effective, but there was some clever stuff at play from what I read!

Of course it’s all in aid of a horribly outdated principle, and I don’t approve of the scare tactics or intimidating nonsense letters, but I can appreciate some clever tech and documentation :)