Abstract: The invention relates to a hearing protection earplug, comprising a shell for being worn at least in part in the ear canal of a user and a faceplate (12) at the outer end of the shell or within a cavity of the shell having an outer opening, wherein the faceplate is provided with adapter means (22) for acoustically connecting, in a detachable manner, a measuring hole (14) extending into the interior of the shell with an external measuring tube (26). The adapter means (22) are adapted to detachably connect to a removable multi-function plug (28, 40) comprising means (30) for closing the measurement hole (14). The invention also relates to a use of such an earplug, a method for manufacturing such an earplug and to a multi-function plug to be used with such an earplug.