Abstract: Described is an improved Temperature Measuring Device which is controllably activatable prior to the making of a temperature measurement from a passive to an active mode; and whose physical display of temperature indication is irreversible, providing a permanent, fixed display as desired. This device consists of a tube which has a reservoir, a rise tube and a means of or a device for creating a discontinuity in the rise tube or between the rise tube and the reservoir. The reservoir contains a solution, the chemical or physical action of which is the basis for the temperature measurement. The rise tube is a containment for the solution when the solution experiences (thermal) expansion or contraction. The means of, or device for, discontinuity is used to impede the expansion or contraction between the reservoir and the rise tube or within the rise tube embodiment.