Something I find really annoying to do is filling up a jug of water. Because the water dispenser lets out the water quite slowly, it takes ages to fill up the jug completely. So I came up with the idea of making a water sensor that will let me know when the jug is full, so I don't constantly have to focus on it.
Because I didn't have very much electronic experience, I made it from trash. To make it I used a cheap kid's toy that I got from a kid's magazine. Basically, it was a small sack that started laughing if you squeezed it. The sound it makes is not perfect, but it works fine. Instead of this any toy that makes a sound when a button is pressed could be used. Happy Meal toys would probably work perfectly.
The two open ended wires are just regular uninsulated 1.5mm wire. I attached it to the toy with some hot-glue (no soldering).
Making this took me just about five minutes. The rewiring was very straightforward, and thankfully there was no soldering needed.How to make it
Remove any covering or casing, so that you can get to the switch. In my case all I had to do was cut off the sack to get to the plastic casing underneath.
Remove or just rewire the switch so there are two open ends. All I had to do was to press the wires onto the switch plates.
Glue (or solder, depending on your toy) the wires down so there are two open wires sticking out
Bend the wires around the casing, making sure that they don't touch. Leave a 1-2cm gap so it can be hung over the side of a jug.
Here's a video of the sensor in action: