Abstract: The invention relates to a passive hearing protection earplug for being worn at least partly within the ear canal of a person, comprising a hard shell (1000) with an elasticity of from shore D85 to shore D65 having an outer surface individually shaped according to the measured inner shape of the person's outer ear and ear canal and being adapted to attenuate sound waves arriving at the outer end of the earplug, further comprising tracing means (1002, 1004, 1006, 1010, 1013, 1014) adapted for being detected by an electromagnetic detector, said tracing means being integrated within or fixed at said shell. The invention also relates to a method for manufacturing and a method for detecting such an earplug.