This article is from the Static Electromagnetic Fields and Cancer FAQ, by John Moulder firstname.lastname@example.org and the Medical College of Wisconsin with numerous contributions by others.
Residential and environmental exposure to static magnetic fields is
dominated by the Earth's natural field, which ranges from 0.03 to 0.07
mT, depending on location. Static magnetic fields under direct current
(DC) transmission lines are about 0.02 mT. Small artificial sources of
static fields (permanent magnets) are common, ranging from the
specialized (audio speakers components, battery-operated motors,
microwave ovens) to trivial (refrigerator magnets). These small magnets
can produce fields of 1-10 mT within a cm or so of their magnetic poles.
The highest static magnetic field exposures to the general public are
from magnetic resonance imaging (MRI), where the fields range from 150-
2000 mT [1,2].
Direct effects on ferromagnetic objects and electronic equipment are the
only things that most people would notice below about 1000 mT. There is
really no threshold for effects on ferromagnetic objects; a good compass
will twitch at fields as low as 0.01 mT, but it takes a much larger
field (above 1 mT) to make ferromagnetic objects move in a dangerous
way. Electronics can be affected by quite low fields; a high resolution
color monitor, for example, can show color distortions at static fields
as low as 0.02 mT.