The Anti-Theft Drawer

The ATL has one drawer everyone needs and nobody trusts. The good screwdrivers live there. So do the two rolls of solder meant to last the whole term, and the box of jumper wires that was full on Monday and half-empty by Wednesday. Nobody admits to taking anything. The lock went missing in March. Your lab has decided to stop arguing and start engineering. The drawer cannot be locked — too many people need it mid-session. So it will not be locked. It will be watched. The moment it opens when it shouldn't, the whole lab will know. That is your brief. Not a lock — a witness. A drawer that reacts the instant it is opened and, if you get that far, keeps its own record of every time it happened, so that "I didn't touch it" stops being something anyone can say. Here is the catch, and it is the whole engineering problem: the obvious way to wire this gives you an alarm that screams while the drawer is shut and goes quiet when someone opens it — exactly backwards. Getting the logic the right way round is the work.