How the presence of a magnetic field checked within a part?

Question

How the presence of a magnetic field checked within a part?

Answer 1

What is the part?  If it has a substantial filed like a triple A batery just pass a dime store compass over it and watch the needle deflect.  If it's a complex system with residual or inherent magnetism it will be more difficult to identify the source.

Answer 2

There is device call Hall effect device that detects the magnetic field.  But you have to build the device.

there's also a TRI-FIELD detector.

http://www.amazon.com/TriField-Meter-Tri...

Good Luck...