How does a thermometer detect temperature?

Matter generally expands as it warms, and contracts as it cools. In liquid thermometers, as the liquid heats and expands, it is directed up a tube with markings to show the exact amount of expansion. In Bi-metal thermometers, there is a strip of two different metals pressed together. These metals expand and contract at different rates. As a result, the strip will coil and uncoil with the rise and fall of the temperature. A needle attached to this coil can show the temperature.