Designing a Santa alarm (honestly)
Adorable.

Frankly, the Little Bits kit is way overkill and incredibly expensive. If your goal is to make a simple sensor that detects pressure and turns on a light bulb, that can be done using stuff you probably have around the house.

Here's a basic idea that might be "good enough" for this year. Next year may require some more sophistication as your son's imagination develops.

Instead of a force transducer pad or something equally expensive, use a metal plate that is propped up by a small spring. When the plate is stepped on, it compresses the spring and makes contact with another plate on the floor. In doing so, a circuit is completed and activates a light source.



The metal plates can be cardboard or plastic wrapped in aluminum foil. Or thin sheet metal. The spring can be an actual spring or any squishable material that deforms enough under the weight of a person (or one jolly fat guy). The whole assembly can be hidden under a rug with only a slight bump giving away its presence.