activate the functionality of the device for example the brushing function of a power toothbrush head or a vibrating function of a battery powered razor for wet shaving the actuator button extends from a stem 18 stem 18 is press fit into a sleeve 20 which slides down when the button is depressed activating the functionality of the device how this occurs will not be discussed as it is not relevant and will differ from device to device the actuator button is returned to its normal non depressed position by a return spring 22 the opening around the sleeve 20 and the adjacent wall 24 of flange 25 of the housing 12 must be sealed in order for the device to be completely water tight sealing is provided by a bellows seal 26 having an upper sealing ring 28 a lower sealing ring 30 and an outwardly bowed bellow 32 upper sealing ring 28 seals against the intersection of the lower surface of the button with the upper end of the stem while lower sealing ring 30 seals against the outer surface of flange 25 under normal interior pressure conditions the bellow 32 resiliently biases the sealing rings against the surfaces they seal against preferably bellows seal 26 is an elastomeric seal that is pre stressed into its sealing configuration by stretching it over the flange 25 when a predetermined interior pressure within the housing is exceeded e g 0 1 to 2 bar indicating the presence of hydrogen gas the bellows seal flexes temporarily breaking the.