Abstract: An inexpensive, disposable apparatus that visually indicates whether an object has been exposed to either one or both of two predetermined critical temperatures such as a critical high T1 or a critical low T2 temperature. The apparatus includes a housing having a reservoir portion, and a capillary tube portion with a first, proximal end in fluid connection with the reservoir portion and an open, second, distal end. A first fluid is contained within the reservoir portion and a portion of the proximal capillary tube portion. A second fluid is contained within the capillary portion intermediate the first fluid and the distal end. A barrier is located intermediate the first fluid and the second fluid. The barrier prevents the first and second fluids from intermixing until the apparatus is exposed to T1 and then allows at least a portion of the second fluid to mix with the first fluid when the apparatus is exposed to T1 and irreversibly changes an observable characteristic of the second fluid.

Abstract: An apparatus that indicates whether an object has been exposed to a predetermined critical temperature T. The apparatus housing has a reservoir portion and a capillary tube portion in fluid connection with the reservoir portion. A first fluid is contained within the reservoir portion. A second fluid is contained within the capillary portion. A barrier is located intermediate the first fluid and second fluid. The barrier prevents the first and second fluids from intermixing until the apparatus is exposed to the critical temperature, and then allows at least a portion of the second fluid to mix with the first fluid when the apparatus is exposed to the critical temperature. An observable characteristic of one of the fluids irreversibly changes when the apparatus is exposed to the critical temperature. The housing completely encapsulates the fluids and barrier within the housing and prevents evaporation of the fluids and barrier from the housing.