Abstract: A low cost device which changes rapidly, significantly, irreversibly, and accurately when it is exposed to a predetermined temperature is disclosed. The device of the present invention employs a bimetallic disk which changes its configuration when it is exposed to a predetermined temperature. Before firing, the disk is captured by a recess in the device casing. When the disk is exposed to a predetermined temperature, it changes configuration and escapes its confinement from its orginal location in the recess. A spring propels the disk from its original location to a different location. Additionally, the spring ensures that the disk cannot return to its original location. This device has a minimal number of parts so that it is easily and inexpensively manufactured. It can be configured to sense either high temperature or low temperature. The low temperature device can be used in conjuction with irreversible temperature labels such that the combination records both a high and a low temperature exposure.