PINs, passwords, secure entry systems; just about everything you access these days needs some form of passive authentication code. Heck, even that Wi-Fi router in your basement uses a mega 63-character password for enabling secure access. Before you know it, you’ll even need a password just to go to bed at night.
Portable Password Generator: [Link]
Electronic combination lock always fascinated me since i was a kid, playing with blinking LED circuits. At that time i was always thinking on some sort of electronic combination lock that i could add to my bedroom door, but unfortunately i wasn’t working with micro-controllers at that time so it was very difficult to put together something like this. But these days you can easily build a project like this, the parts are available everywhere.
Electronic combination lock with AT90S2313 or ATtiny2313: [Via] - [Link]