Simple bimetallic thermostats combine two strips of metal having different coefficients of expansion joined together. When the strip is heated the different expansion rates of the two metals causes the strip to bend and this can be used to operate an electrical contact. Simple preset devices are usually used for over-temperature protection e.g. domestic fan heaters and automatic kettles, burnout for electric motors, etc. They can also be used as preset thermostats for controlling temperature. This experiment illustrates the use of a bimetallic strip sensing element to control temperature.