Kids design and build magnetic-field detectors and use them to find hidden magnets in this activity from Design Squad Nation. They also learn how NASA uses magnetometers to learn what is going on inside a planet or moon. People love treasure hunts. But, in this one, kids are looking for something invisible! As they build their mmagnetic detectors, the kids use the engineering design process, apply a variety of science concepts (e.g., force, magnetic fields, mapping), and learn how a planet's or moon's magnetic field gives NASA scientists insights into its structure and how it formed. This resource is useful for introducing components of Engineering Design (ETS) from the Next Generation Science Standards (NGSS) to grades 3-8 students.