And speaking of telephone mischief, here’s a Dianatek model 041 pen register, designed for use not by law enforcement, but by telephone companies. The telco security department would hook this up to your line (at the central office) if you were suspected of making harassing calls or otherwise misbehaving with your service. It also detects signals used by blue boxes, despite being made well after they were obsolete. Resembles a movie prop bomb that starts a short countdown when you open it.