I thought about building a box that auto-locks when the weight of a package is detected in it. Can be a simple flap on the bottom that moves a latch. The lid

I thought about building a box that auto-locks when the weight of a package is detected in it. Can be a simple flap on the bottom that moves a latch. The lid would be a double lid -- an outside lid with a key lock, and the inside frame that the flap-activated latch slides into.