I built a digital alarm clock based on those two-key activation sequences that we can see often in movies (and in real life too, sometimes). So, in order to turn off the alarm you need to perform one of those actions and also input a code using a keypad.
It's made around an Arudino Mega with a bunch of leds, buttons and some extra stuff like an Real Time Clock module. Here's the full code that runs all the system.
A more extended report, along with extra pictures can be found in my website.
