Will a magnetic case ruin my new phone?

I recently purchased a Samsung Galaxy smartphone and want to buy a protective case for it for when I'm out and about. Most of the cases I have seen have a magnetic button to keep the phone securely inside the case. However, I am concerned that it is not safe to have a magnet that close to the phone, and have found conflicting advice online. Do you have any advice as to whether a magnetic clasp would be safe?

Johanna Coulson, by email

It is not a problem, insofar as damaging your smartphone is concerned, but a magnetic clasp could have other, unexpected consequences. To begin with I would keep it well away from any credit or debit cards with magnetic strips as it could erase or corrupt the data they contain. Almost all smartphones and many tablets have a tiny built-in magnetic sensor; some have two. The most common type is a magnetometer or Hall Effect device that is used by compass apps to point the way towards magnetic North. The other type, fitted to some Android tablets and Apple iPad 2 onwards, works in conjunction with a tiny magnet embedded in the case. This turns off the display and put it into sleep mode when the cover is closed. Clasp and case cover magnets are generally quite weak but when bought in close proximity to the phone or tablet may affect compass readings. So be warned, if you plan to use a compass app for some serious navigation, remove the case and keep your device well away from any magnets.