Adafruit HD Magnet Viewing Film - 50x40mm [ADA4047]
Add extra-sensory powers to your toolkit with this nifty piece of HD Magnet Viewing Film . It's a special film that contains a ferromagnetic slurry of ultra small nickel particles that turns black when around a magnetic field. Unlike some of the older films you may remember from grade school science class, this stuff is 'high resolution' so you can really see the details.
Slide it over enclosures and devices to locate hidden magnets and speakers. Comes laminated for protection.