Magnetic recordings on tape, cassette or disc are made and destroyed by magnetic fields. The permanent magnets in headphones and compact loudspeakers can produce a strong magnetic field which may damage the tapes if they are stored in close proximity.
Normal house wiring is not usually a problem, however high voltage power lines and lightening arresters in large buildings can produce dangerous levels of electromagnetic interference. Security scanners and X-ray equipment aren’t usually harmful, but it is wise to check first, particularly with newer digital systems.
The most likely articles found in the home that can affect tapes are those with small powerful magnets, for example, magnetic flashlights, fridge magnets, small headphones, speaker cabinets etc.
CDs are not affected by electric or magnetic fields.