Information about individual devices and dangers
There are expensive and cheaper versions when it comes to
cards with magnetic stripes ("magnetic cards").
High-quality magnetic stripes can be found on credit
or ATM cards. They are dark-brown or black and it takes 0,4
tesla (0,4 tesla = 400 mT = 4000 gauss) to demagnetise these
But already a third of this field strength is enough to partially
delete magnetic stripes so that they can't be properly read
anymore. At a tenth of the demagnetisation field strength (coercive
field strength), meaning 40 mT, there is no danger of damages
Cheaper magnetic stripes are light-brown and frequently
used on parking garage or admission tickets. These stripes are
much more sensitive. It takes only 30 mT to demagentise
Field strengths of up to 3 mT certainly do not cause any harm.
Pacemaker and Heart Defibrillator
A pacemaker or heart defibrillator is implanted in people
with heart rhythm disturbances. These devices are implanted
under the skin in the chest area. They produce electrical impulses,
which regulate the activity of the heart, if the patient's body
cannot produce these regular impulses itself anymore or if cardiac
A static magnetic field can cause pacemakers and heart defibrillators
to switch into special mode. The characteristics of special
mode can be programmed and are determined by the manufacturer.
A physician can initiate a controlled switch into special mode
with a strong permanent magnet. He does that to;
- Control pacemaker and heart defibrillator
- Set a determined frequency for some cycles (independent
from the actual need of the body)
- Disable certain functions of the defibrillator
As soon as the magnet is removed, the pacemaker or heart
defibrillator starts working normally again.
Newer pacemakers switch into special mode at 1 mT, older
models already at 0,5 mT (=5 gauss). Therefore, you need to
adhere to the safe distances to permanent magnets outlined in
the table above.
However, we cannot offer you a magnet that can purposefully
switch a pacemaker into special mode, since this depends on
the device and is beyond our knowledge as a magnet retailer.
A strong magnetic field can magnetise parts of mechanical
watches, like for instance the spiral spring. The parts then
react to other steel parts in the clockwork or to the clock
case. This may lead to the watch being fast or slow.
Most of the standard watches now follow the ISO 764 standard
and are "non-magnetic". Such watches need to
be able to resist a magnetic field of 60 gauss (=6 mT), which
means that after being exposed to this magnetic field they can
only be off by a maximum of 30 seconds per day. Some manufacturer
offer especially designed non-magnetic watches that can withstand
up to 1,000 gauss.
It is difficult to indicate a safe distance for non-magnetic
watches. If you want to be on the safe side, you should
keep as much distance for the magnetic field to equate only
to the natural Earth's magnetic field of about 0,05 mT.
If a mechanical watch was magnetised by accident and doesn't
work properly anymore, you can bring it to a watch maker. He
can demagnetise it with a special demagnetisation device, which
creates an alternating magnetic field.
Analogue quartz watches can be disturbed by a strong
magnet, because the strong magnetic field interferes with the
motor. They might all of a sudden be fast, slow or stop working
altogether. But as soon as the magnet is removed and the time
is corrected, the quartz watch should be working normal again.
The following components of modern hearing aids may react
to static magnetic fields:
- The speakers
- The coils responsible for the wireless communication
between two hearing aids or between hearing aid and remote
A magnetic field strength of 200 mT or above can cause permanent
A magnetic field strength from 20 to 200 mT can cause temporary
malfunction which may include:
- Distorted acoustic signal
- Strongly reduced remote control reach
- Collapse of the bidirectional radio link hearing aid
or hearing aid accessory
A static magnetic field does not damage a vehicle key or
the embedded transponder for the anti-theft device. Therefore,
you can hang up your vehicle key on a magnetic board.
USB Stick, Memory Cards (Compact Flash, Secure Digital,
USB sticks and memory cards are not magnetic data carriers
and will therefore not be damaged by static magnetic fields.
Digital Camera, Cell Phone, iPhone, iPod, iPad etc.
Cameras, cell phones and smart phones contain non-magnetic
storage media. Therefore, static magnetic fields near those
devices cannot delete data.
There are countless covers with magnetic closures or magnetic
holders on the market, which also speaks against the notion
that magnets can damage these devices.
However, it cannot be ruled out that very strong magnetic
fields might magnetise and maybe damage mechanical parts or
built-in speakers. When in doubt, keep these devices away from
CDs and DVDs sticks are not magnetic data carriers and will
therefore not be damaged by static magnetic fields.
You can find much contradictory information regarding this
topic. Hard drive manufacturers themselves don't like to talk
about it. But generally, hard drives are much more resistant
to big magnets than expected. The hard drive coating usually
provides a high level of coercivity. This means you would have
to bring a very large magnet very close to a hard drive in order
to delete files. As long as you don't unscrew the top cover
of the hard drive, you won't be able to get close enough. A
strong magnetic field, however, can damage mechanical components
of the hard drive. A magnet can, for instance;
All the above may lead to irreparable damages.
- block the motor of the reading head
- influence the position of the writing head or
- damage the writing head
Hard drive of a desktop computer: A magnet is hardly
a danger for hard drives embedded in a desktop computer, because
you cannot get close enough. Compact laptop hard drives, however,
which are generally located near the bottom plate, are more
sensitive towards permanent magnets. We cannot provide safe
distances due to insufficient data and differing construction
of hard drives, but even our biggest magnets should not be able
to damage a hard drive at a distance of 20 cm.
Intentional deleting: If you plan on deleting data
on a hard drive permanently, using a permanent magnet is not
a suitable method. You can use special file deletion software,
which overwrites the hard drive multiple times