AEA Amatrol's Sensor Logic Systems Practice Test

The main idea here is that a sensor is the device that detects a physical condition and turns it into an electrical signal for the system to read. The description “electronic assembly that includes the circuitry and components that detect presence” matches how a sensor works: it senses presence (a person, object, etc.) and outputs a signal that can be processed by controls. A transducer is a broader term for any device that converts energy from one form to another, and while many sensors are transducers, the specific role described—detecting presence—points to a sensor. An actuator does the opposite: it uses an electrical signal to produce motion or some action. A relay is essentially a switch that's driven by a signal to open or close circuits, not something that detects presence itself. So, the term that fits best is sensor.