The Babington Plot was a famous conspiracy, in 1586, to assassinate Queen Elizabeth. It led to the execution of Mary Queen of Scots, whose weak cipher implicated her. Check out that cipher today, cryptography fans!
Remember those plastic glasses we had as kids, which changed color if liquid was inside? You'd quite often get them for 99c with a kid's meal at a fast food chain. These are the next (grown-up) step in the evolution.