Nice rice

One of my housemates has a rice cooker he brought over from Sri Lanka (he's a bit of a rice fan). The design is relatively simple - a metal bowl stood on top of an electric conductive heating element.

However the bowl sits on top of a weakly-sprung platform which raises it above the level of the heating element. When the bowl is empty the spring can push it upwards. Once the bowl is full of water the spring can't hold it up any more so it makes contact with the element and a switch inside the heater is tripped.

This simple mechanism prevents the heater from switching on whilst the bowl is empty, which would most likely damage the heater. As soon as sufficient water is put into the bowl to remove this danger, the heater's simple sprung switch trips allowing the water to be heated.

Brilliant! (And tasty).