Temperature

Thermocouples are made of two conductors and the temp affects the voltage differential, which is measured. These are often good enough, but not highly precise.

RTD is a resistance temperature detector using a pure metal like platinum that has an accurate relationship of resistance to temp. Related to this, we also have thermistors which are resistors whose resistance is dependent on temperature. In some cases, rather than detecting temperature, a thermistor is used to change a circuit based on the temperature fluctuations.