Thermopiles convert thermal energy into electrical energy. Thermopiles use several thermocouples connected in series or parallel. Thermopiles are used for contactless temperature sensing. The function of a thermopile is to transfer the heat radiation emitted from the object to a voltage output. The output is in the range of tens or hundreds of millivolts.

Thermopiles work as sensors or generators.

As a sensor, the thermopile is used to determine a relatively low temperature (compared with normal thermocouple operations). Applications for thermopile sensors include appliances such as microwave ovens, clothes driers, medical devices, automotive (car climate control, seat occupancy, blind spot alert, black ice detection), consumer products (printers, copiers, mobile phones) and many other applications.

A thermopile generator generates electrical energy from heat. A typical application is flame failure. In a gas water heater, gas fireplace or gas stove a thermopile generator produces voltage while a pilot light is lit. Once the pilot light is extinguished, the voltage drop triggers a valve shutting off gas supply to the appliance.