What is the device called that indicates temperature changes by its response to volume or pressure changes?

The device that indicates temperature changes by responding to volume or pressure changes is known as a Bourdon tube. This device operates on the principle that temperature variations can lead to changes in pressure within a gas or liquid. As the temperature increases, the gas expands, causing the Bourdon tube to uncoil or straighten, which in turn moves a pointer along a calibrated scale to indicate the pressure change. In applications where temperature is measured indirectly via pressure, the Bourdon tube serves as a reliable indicator.

Other devices listed have distinct functions. A pressure gauge specifically measures the pressure of a fluid and does not directly indicate temperature changes. A thermocouple measures temperature based on the voltage generated at the junction of two different metals but does not rely on volume or pressure changes. A manometer measures the pressure of gases or liquids; while it does relate to pressure, it does not inherently indicate temperature changes through volume or pressure variations. Thus, the Bourdon tube is uniquely suited for the context of this question.