What does a temperature sensor primarily detect?

A temperature sensor primarily detects heat, which is a measure of the thermal energy of an object or environment. The functioning of temperature sensors relies on the physical properties of materials that change with temperature. For example, thermocouples measure the voltage that develops across two different metals in response to a temperature difference, while thermistors change resistance based on temperature variations.

Understanding that temperature sensors are specifically designed to quantify heat makes it clear why this option is the most accurate. The other choices represent different types of sensors: light levels are measured by light sensors, gas pressure by pressure sensors, and water vapor by humidity sensors, all of which are distinct from the function of a temperature sensor.