Improve upon the boring design of most wire hamster cages using electricity.
I plan to use fans to provide air circulation, LEDs for lighting, a pump for automatic water bottle filling, and a buzzer for an open cage door alarm.
I purchased a 12VDC power supply from Radio Shack to power the whole setup. I already had the other necessary parts from salvage for the lighting and air circulation. I used 5 470ohm 1/4W resistors in parallel to provide resistance to protect 5 green 20mA LEDs from excessive current. I wired the fans up to a light-up switch in parallel and attached them to opposite sides of the cage, one flowing in the cage and one flowing out for maximum air flow. The five LEDs were superglued into a cardboard box that i fashioned into a makeshift shelter for the hamster. To prevent the hamster from chewing the wires i ran them along the outside of the cage where they are inaccessible from the inside.
Installing the cage door alarm was a simple matter. I bought a normally-closed push button switch and simply wired it to a buzzer and the 12V power supply. I then attached the buzzer to the cage, such that the button was pressed when the cage door was closed. When the door opens, the button is released and the alarm sounds. I was afraid that slight jolts might set off the alarm, but the push button needs to be at least 1/3 of the way out to complete the circuit, so this did not end up being a problem. With this installed, the cage is almost as secure as a state prison.
I purchased a windshield washer pump for a few bucks and I will probably work on the plumbing system pretty soon. I found a motor that will work great for the wheel generator, which I will hook up when I find the motivation.
Update: I no longer keep hamsters, but I may decide to "trick out" my rats' cage at some point. A siphon system to refill the water bottle would be the first step. Rats seem to chew and urinate a lot more than hamsters so that could make any electrical wiring hazardous.