We learned/discovered that an Atari 2600 cartridge was the right size for a 9v and step transform to house in a snug little package after removing the game cart itself. After adding a couple of leads to the open end, a button on the back side, you could "show" some unsuspecting friend your new game while leading up to the shocking game play.
Back in middle school, like 1981-ish I had this hardback book with a title of something like "A Shocking Story". The inside was hollowed out to hold about the same but it was rigged to go off when you opened the book. It got confiscated.
Thinking back, we were really bored