The Tripods

A few weeks ago I purchased a box set of an old BBC TV series called The Tripods. I didn't watch it when it was originally broadcast in the 1980s. It was adapted for television but was originally a series of books.
The series features robotic tripods and non-humanoid aliens. It seems to be set in a state that is kept artificially primitive. The people are subjugated and when they reach 15 are given a "cap" by the Tripods, which is a triangular "chip" burned into their head. This inhibits their creativity and curiosity and keeps them under control.
It is worth watching as a TV series but it doesn't really compare to todays science fiction series.