Have a look at these two cool Secret Box projects that PICing4fun has uploaded. They were created years ago but he just recently got them online. They are both built around PIC microcontrollers and the code was written in native ASM machine language. The first one is a 6 sided box in the form of a dice, you need to roll the dice in a way that a certain pattern of number presented on top to open the box. The second looks for a knock sequence to open the box. The knock box is unlocked by a stepper motor and I was actually surprised to see the project being powered by only a few coin cells.