Magnetometers

"A magnetometer is a device that measures magnetism—the direction, strength, or relative change of a magnetic field at a particular location." -- https://en.wikipedia.org/wiki/Magnetometer

"A fluxgate magnetometer consists of a small magnetically susceptible core wrapped by two coils of wire" -- https://en.wikipedia.org/wiki/Magnetometer#Fluxgate_magnetometer

MEMS. "Development of Resonant Magnetic Field Microsensors: Challenges and Future Applications", https://www.intechopen.com/books/microsensors/development-of-resonant-magnetic-field-microsensors-challenges-and-future-applications