Do you worry about your recordings being affected by magnetic fields?
Perhaps you should worry about magnetic fields.
There are magnetic fields all around. Fortunately, the Earth's field is too weak to affect recordings. But electric motors emit strong fields (watch out where you sit in an electric train - you could be sitting on top of a motor). So do loudspeakers. And sometimes technicians like to carry magnetized screwdrivers around with them - great for picking up screws, but death to some types of recording.
What types of recordings can be damaged? The most sensitive are analog recordings. The tape has a low coercivity meaning that it is very sensitive to magnetic fields. NEVER put an analog tape on top of a loudspeaker.
Digital tapes however are very much more robust. You are unlikely to damage a DAT tape anywhere in the studio, but loudspeakers still really should be a no-go area just to be sure. Even if a DAT tape is not audibly affected, the error rate may be higher and further use and abuse could just push it over the top into glitching.
Hard disks too use magnetism to store data, but the coecivity is high so they are likely to be safe, but best to be careful.
Some digital storage devices use magneto-optical technology, such as Minidisc. However, the surface is only sensitive to magnetism when heated by a laser, so they will not be damaged at all by external magnetic fields in normal use.
One last thought - remember to take off your watch when using a bulk eraser (device for erasing tapes a whole reel at a time). Certain types of watch will run at up to 60 times their normal speed!