How to explain the behavior of the magnetic field sensor?

Question

Sensors

I have a Samsung i777 phone (aka Galaxy S2 AT&T). The phone has a magnetic field sensor. Recently installed the SmartTools app, it has a magnetic field measurement function. While playing, I discovered a curious thing: from some objects, the sensor really rolls over. Among them, for example, cell phones. But not all - out of the five tested, only three went off scale, the levels are different. Moreover: two phones of the same model, on one it goes off scale, on the other the reaction is minimal. Tried to pull out of one of these off-scale battery - nothing changes. No, of course, I understand that all cell phones have a speaker, and the speaker has a magnet. But why such a difference even within the same model?
A similar story with a radio-controlled micro-helicopter - rolls over. Well, yes, there are engines. But at the same time, the sensor reacts much less to the fan, where the engine is much larger.
All tests were carried out several times from different edges. The result is somehow stable.
Actually, it's curious. If someone understands the topic well, please explain why this is so?

Answer 1

You were right, it's because of the magnets in the speaker/motor. Not any magic.

Answer 2

The phone sensor is not designed to measure such a strong field (beyond the measurement limit).
Yes, and the dynamics can be slightly different.