After years of using Rube Goldberg-inspired projects to teach concepts of simple machines, the author sought a comparable project to reinforce electricity lessons in his ninth-grade Science and Technology course. The Friendship Detector gives students a chance to design, test, and build a complex circuit with multiple switches and battery-powered lights or buzzers. The process involves important engineering themes and core scientific content. Unlike electronics kits, with supplied parts that must be assembled precisely according to instructions, the Friendship Detector can be built with objects found around the home. Students must make value judgments while wiring the project, resulting in a circuit design unique to each student. Developing a mental model of circuits is often quite challenging. The Friendship Detector project, detailed in this article, approaches this challenge in a variety of ways, appealing to different learning styles and building competencies in nonpreferred styles. (Contains 6 figures and 1 online resource.)