A device for measuring temperature that makes use of the way different metals respond to heat.
Example:
Thermocouples can be used to measure temperature as high as 2300 degrees Celsius or as low as -270 degrees Celsius, far beyond the range of ordinary thermometers.
Thermocouples use wires made of two different metals, such as copper and iron. The wires are joined at both ends; one end is placed against the object whose temperature is being measured, while the other end is kept at a known, constant temperature. The thermocouple generates a voltage that depends on the difference in temperature between the two joined ends of the wires and can be measured to obtain the temperature of the object.