A data entry device including a housing formed of at least two portions, data entry circuitry located within the housing, at least one case-open switch assembly operative to sense when the housing is opened and tamper indication circuitry operative to receive an input from the at least one case-open switch assembly and to provide an output indication of possible tampering with the data entry circuitry located within the housing. The at least one case-open switch assembly includes an arrangement of electrical contacts arranged on a base surface and a resiliently deformable conductive element, which defines a short circuit between at least some of the arrangement of electrical contacts only when the housing is closed.