Patent ID: 7770534

Claim:
A device for indicating a transition across a threshold temperature comprising: a housing; a first surface, at least a portion of said first surface being of a first color; a first reactant located on said first surface within said housing; a capsule containing a liquid and a second reactant, said capsule being located within said housing; wherein said liquid freezes at a first threshold temperature and expands upon freezing whereby said capsule fractures from the liquid expansion; wherein said first and said second reactants combine on said first surface to produce a pigment of a second color upon mixing, said first and said second colors being different; and wherein said first reactant and said second reactant are salts of a weak acid-strong base and a strong acid-weak base, respectively; and further comprising a second capsule located within said housing and optionally a third reactant; wherein the formulation of said second capsule comprises a component that melts at a second threshold temperature; wherein said second capsule contains said second reactant or said optional third reactant; wherein when said optional third reactant is present, said third and first reactants combine to produce a pigment of a third color upon mixing, said third color being different from said first color; and wherein said third reactant is a salt of a strong acid weak base.