Fire alarm

A bimetallic strip consists of two metal strips riveted or welded together in the longitudinal direction. The two blades are made of two different metals having different coefficients of thermal expansion. A variation in temperature causes a deformation of the bimetal. The deformation is all the more important as the length of the bimetallic strip is great. This is what can be observed on bimetals coiled in a spiral.

Since these are metals, it is sufficient that one of the two is a good enough conductor to be able to exploit this property in an electrical circuit. The bimetallic strip then becomes a switch that reacts depending on the temperature. There are bimetallic strips in circuit breakers, fire alarms, blinking bulbs and thermostats.

See also the eduMedia animation bimetallic strip.