Magnets and electronics: phone, bank card and laptop
Short answer: a neodymium magnet will not break a smartphone, laptop, SSD or USB stick. A strong magnet can, however, erase a magnetic stripe on a card or hotel key, disturb a phone's compass and camera stabilisation, put a laptop to sleep and make a mechanical watch run inaccurately. Chips and contactless payment keep working. Keep strong magnets at least 15 cm from a pacemaker.
Overview per device
| Device | Risk | Advice |
|---|---|---|
| Smartphone | no damage to memory or screen; compass and optical image stabilisation (OIS) can be temporarily disturbed | no strong magnet directly against the camera; recalibrate the compass if needed |
| Bank card, credit card | chip and contactless: no risk; magnetic stripe can be erased | do not keep cards directly against a neodymium magnet |
| Hotel key, parking ticket, card with stripe | low-coercivity stripe, erased quickly | keep away |
| Laptop, tablet | the lid sensor can switch off the screen; no damage | do not place a magnet on the edge near the keyboard |
| Hard disk drive (HDD) | very small risk with an ordinary magnet outside the case; a very strong magnet directly on the case can interfere | no large magnets on a running HDD |
| SSD, USB stick, SD card | no risk; flash memory is not magnetic | no action needed |
| Mechanical watch | the hairspring can become magnetised, so the watch runs fast or slow | a watchmaker can demagnetise it |
| Compass | can be permanently reversed | store separately |
| Pacemaker, ICD, insulin pump, hearing aid | can switch to a different mode | at least 15 cm distance; see are neodymium magnets dangerous? |
| Old CRT TV or monitor | colour patches | keep away |
Why doesn't a magnet break a phone?
Modern phones store data in flash memory, which does not work magnetically. Phones themselves contain magnets: in the speaker, the vibration motor and, in many models, a magnetic charging ring. What is sensitive: the magnetometer (compass) and the tiny motors that stabilise the camera. A strong magnet directly against the lens can temporarily disturb that stabilisation. Manufacturers therefore advise against mounting phones with a loose strong magnet, unless the holder is designed for it.
Why does a magnet erase a card?
A magnetic stripe stores data as tiny magnetised areas. A strong field can overwrite them. Bank cards usually have a high-coercivity (HiCo) stripe that is harder to erase, but a neodymium magnet in direct contact can do it. Hotel keys often use low-coercivity (LoCo) stripes and can be erased by a bag with a magnetic clasp. The chip and the contactless antenna are not sensitive to magnets. More about coercivity in what is coercivity (Hc)?
Tips for magnets in bags, sleeves and holders
- A small sew-in magnet in a bag or phone case is no problem for phones and chip cards. Keep cards with a magnetic stripe away from the clasp. See sew-in magnets in bags and laptop sleeves.
- For a magnetic phone holder in the car: choose a holder designed for phones.
- Do not store loose strong magnets in the same drawer as watches, compasses and hotel keys.
Frequently asked questions
Can a magnet damage my laptop?
No. A laptop with an SSD has no magnetic memory. A magnet near the edge can trigger the sensor that switches off the screen when you close the lid.
Can a magnet erase a hard drive?
Hardly in practice: the platters have a high coercivity and sit inside a casing. Real erasing is done with a special degausser. Still, do not place large magnets on a running hard drive.
Is a magnet bad for my phone battery?
No. A magnet has no effect on the battery.
