If you want a way to measure magnetic fields on the go, then look no further than this tiny device from Instructables user “rgco.”
The portable magnetometer was made using just a couple of common parts, including an SS49E linear Hall effect sensor, an Arduino Nano, a 0.96” OLED screen, and a push button.
All the electronics are concealed inside a Tic Tac box, which holds the components together and provides a window for the display. The SS49E itself is isolated from the rest of the unit via a ballpoint pen tube, which allows it to be placed in narrow openings without interference.
For increased accuracy, the sensor was calibrated using a cylindrical electromagnet, and the project was prototyped using an Uno before being stuffed into its rather small enclosure.