Abstract: Device for detecting the exceeding of a temperature threshold incorporating a first mobile part (5) in a sealed chamber (4) containing a material melting at the temperature of the threshold and a second mobile part (8) outside the chamber. In the armed position, the two parts exert forces on one another tending to move them apart, but the first part is blocked by the solidified material and the second is immobilized by the combination of shapes (12, 13) in case (9). The melting of the material frees the first part, whose displacement frees the second part, which then operates an alarm system (18). This displacement leads to the return of the first part to the initial position, which permits rearming when the material has resolidified.