sensor

This term describes the bridge between the physical world and digital data. It implies a passive state of waiting for a specific trigger, such as heat, light, or motion, before converting that physical stimulus into an electrical signal. In modern usage, the word is heavily associated with automation and surveillance. While a detector might simply alert a human, a sensor is typically integrated into a larger system that can take autonomous action, like a thermostat adjusting the temperature based on a temperature sensor.