Abstract: A switch assembly including a base member having a contact receiving cavity open at the top and defined by a floor that is laterally enclosed by side wall means, first terminal means in the cavity adapted for electrical connection to outside circuitry, second terminal means in the cavity adapted for electrical connection to outside circuitry having a resilient contact blade portion with an end above the first terminal means. The contact blade portion is moveable between a normally open position wherein the end is spaced from the first terminal means in a closed position wherein the end contacts the first terminal means. A thin, stretchable, resilient, impermeable sealing gasket is provided on the base member which ovelies the cavity. A cover engages the periphery of the gasket and includes interengaging means cooperating with the base member to lock the covering gasket to the base member to form a hermetic seal over the cavity.