Paul sez, "torrentfreak.com has an excellent post describing what must be one of the first DRM devices evar. the Lenslok is a foldable optical lens that was required to decipher scambled unlock codes in early 1980's video games. from the torrentfreak post:"
The first game to use the Lenslok DRM was the ZX Spectrum version of the hugely successful wireframe-3D shoot 'em up, 'Elite'. But of course, we're talking about DRM here so yes, you guessed it, it caused lots of problems for the legitimate users. As each version of the Lenslok device was unique to the game it sought to protect, sending out the incorrect Lenslok device to around 500 buyers of 'Elite' wasn't the best move made by the publisher, 'Firebird'. None of these people could play the game, but probably had an interesting experience for a few hours trying to work out how to use the prism. With no Internet forums to voice their anger, there were many complaints in the computer magazines of the day.
The final nail in the Lenslok coffin was its inability to work with anything other than a tiny portable TV, as the on-screen input window would otherwise be bigger than the device itself, rendering it useless.