Abstract: The present invention relates to a device for monitoring a temperature variation undergone by a product, which detects a drop in temperature below a predetermined temperature threshold (Tcs), comprising: a sealed casing (I) which defines a containment space (V), and a mixture contained, or containable, in said containment compartment (V) which comprises a liquid phase (S) and a solid (D) comprising metal particles having an average nanometric size comprised between 1 and 300 nm and a coating layer (R) of said particles.