These days, parental locks stop kids from playing games using simple software. In 1990, lacking that kind of technology, things were a little more draconian.
This is the "Homework First" video game lock, designed for the NES. It does not fuck around. Looking like a very hefty bike lock, it hooked underneath the console and pried the cartridge door open, meaning that unless you wanted to trash the casing of the NES, games couldn't be played while it was engaged.
What's even more amazing than the product itself is the marketing campaign to sell it, which involved use of the word "Nintendonitis". My hat goes off to EW's archives for keeping stuff as far back as 1990:
To prevent what it calls ''Nintendonitis'' — irritability and obsessive behavior — Safe Care Products Inc. is selling Homework First, a lock for Nintendo games that blocks the opening of the cartridge compartment. Safe Care president Tom Lowe invented the 15.95 device after hearing that a friend's 14-year-old son stayed up all night playing Nintendo instead of studying for finals. Homework First has received endorsements from a pediatrician and the Council for Children's Television and Media. Nintendo refused to cooperate with Lowe, but he has sold about 25,000 locks in toy stores and by phone (800-235-6646, ext. 480).
What an age it was.