Solar panels are an amazing invention. Catching energy from the Sun before it even enters Earth's food chain, photovoltaics are like an all-natural nuclear power plant. Unfortunately, the constituted parts of a solar panel are rare, valuable, and subject to the coercive forces of market competition.
Just about every household gadget we own runs on 1.5 volt batteries of one size or another. Wouldn't it be great if you could reuse all of those dead AA, AAA, and D batteries after they've passed on? It turns out you can make a simple circuit called a "Joule Thief" to reanimate the undead flesh of your deceased batteries and create a zombie battery.
There is nothing more annoying than a greedy roommate. It's absolutely infuriating to wake up and find the cookies your mother just made for you gone without a trace. Your favorite drink is empty and the homemade meal you worked so hard on the night before is nowhere to be found. This irked me so much that I made this shocking cookie jar. When a cookie burglar touches the side and the lid of the jar simultaneously, a small electric shock stops them in their tracks.