To my surprise it actually works!…It’s far from working perfectly… but it can detect if something is metal or magnetic! Not the most accurate but it does work
Magnetometer is a fun app for finding metal or magnets by detecting EMF interference with your iPhone's compass heading. Find your keys, or just have fun discovering what could be made of metal. Magnetometer is not meant to replace an actual, professional-grade metal detector. Magnetometer presents simple information to the user about the interference experiences. For more scientific data, please turn to other great apps on the App Store. Magnetometer is made for fun and for experimental purposes and is not designed for scientific use. Also, don't drop your iPhone in sand hoping to find treasure; it's risky.