https://en.wikipedia.org/wiki/Magnetic_implant

Magnetic implant is an experimental procedure in which small, powerful magnets (such as neodymium) are inserted beneath the skin, often in the tips of fingers. They exist in tubes and discs. This procedure is popular among biohackers and grinders, but remains experimental.[1] Magnetic implants are often performed by amateurs at home, using readily available surgical tools and magnets found online. However, some professional body modification shops do perform implant surgeries.[2] Magnetic implants can also be used as an interface for portable devices to create other new “senses”, for example converting other sensory inputs such as ultrasonic or infra-red into a touch sensation.