Might be of some use for magnet strength comparison

[Sock Puppet]

and even more use if it's calibrated, a couple of Android apps:

https://play.google.com/store/apps/d...r.sira.compass

https://play.google.com/store/apps/d...detector&hl=en

Apologies if this has all been covered but I don't get round here often.

[eschertron]

Great Topic! I just downloaded the "Magnetic Field Detector" app from Mobile Development Team. More fun !!

[LtKojak]

I wonder with WHAT is the phone reading a magnetic field?

Is there a hall-effect probe inside every cell phone? What is it used for anyway?

EDIT: my phone, a Brondi Glory2, doesn't have such a sensor. No app work with it. DAMMIT!

[David Schwab]

My iPhone can do this, but be very careful. The magnet sensor is not meant to read the strength of magnets, and you can screw it up if you put a very strong magnet near the phone. Personally I wouldn't bother with it.

[Sock Puppet]

All I can say is that I've had strong NdFeB magnets next to my cheap HTC Wildfire S phone and I don't believe it's affected the magnetometer. The compass app above still points north. YMMV