Permanent magnets are used as automatic temperature control switches at the bottom of traditional electric rice cookers, a pair of strong ring permanent magnets are used for magnetrons in microwave ovens, and permanent magnets are used for speakers and earphones of audio equipment (including mobile phones). 

The automatic temperature control switch in the middle of the bottom of the old electric rice cooker uses a permanent magnet. The magnetron in the microwave oven uses a pair of ring permanent magnets with strong magnetism. All audio equipment (including mobile phones) has permanent magnets in speakers and headphones.