Resource conservation is very important. Annually, a huge amount of resources are wasted for often trivial reasons - someone leaves the tap running for too long, leaving the lights in the room on after exiting it, etc. So at the code club we decided to build a 'smart refrigerator' (well, a model of a smart refrigerator) that beeps when the door is open to alert the person and make them close the door, which saves electricity.
The Micro Bit has Light sensors on the LEDs that enable it to detect the intensity of light (darkness/light). The project I had originally proposed to the students involved switching on an LED and Buzzer when the light level inside the refrigerator door increased, and shutting off the LED and Buzzer once the light level decreased.
The Student Modification
The students however, came up with their own hack. They used a bit of Aluminium foil on the hinge of the refrigerator, and made a switch that switched on the LED whenever the door was open. When the door is opened, the aluminium hinge folds on itself, and completes the circuit and switches on itself, no micro:bit required! However they still needed to implement the buzzer, so they measured the light level from the LED, and then set the buzzer to work. The refrigerator ended up working more or less how I envisaged it to work.