Abstract: An improved probe cover and thermometer for tympanic temperature measurement include means to preclude the reuse of a probe cover. In the preferred embodiment, a cup-shaped probe cover includes two or more legs terminating in tabs or flanges. The tabs or flanges are sensed by switches. In the preferred embodiment, the switches are disposed within a recess, thereby precluding the circumvention of the switch function. In an alternative embodiment, a plurality of externally located switches are provided to mate with a plurality of flanges. Alternative, the extension from the probe cover may comprise a skirt terminating in a flange or tab. In operation, the thermometer may not be operated without the positive presence of a probe cover, as indicated by the presence of the tabs acting upon the recessed switch or a plurality of tabs acting upon the externally located switches. Ejection of the probe cover causes deformation of the probe cover to indicate prior use.