Lenslok

It was created by John Frost, an inventor and electronics consultant, and marketed by ASAP Developments, a subsidiary of J Rothschild Holdings.

[3] The Lenslok device was essentially a row of prisms arranged vertically in a plastic holder.

By viewing these bands through the Lenslok they were restored to their correct order and the code could be read and entered allowing access to the game.

[4] The device was small enough when folded flat to fit next to an audio cassette in a standard case.

[2] Additionally, the device could not be calibrated at all for very large and very small televisions,[5][3] and some games shipped with mismatched Lensloks that prevented the code from being correctly descrambled.