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 including an arrangement of electrical contacts including at least first, second and third contacts and a displaceable conductive element, the tamper indication circuitry and the third contact together being operative such that when the third contact is short circuited to at least one of the first contact, the second contact and another contact, an output indication of possible tampering is provided.