A bi-metallic strip is a device made of two different metals bonded together. When the temperature changes, each metal expands or contracts at different rates, causing the strip to bend. This bending can be used to measure temperature or activate switches in various applications. Bi-metallic strips are commonly found in thermostats and temperature sensors. For example, in a thermostat, the bending of the strip can open or close a circuit, regulating heating or cooling systems. This simple yet effective mechanism is crucial for maintaining comfortable indoor environments.