An outdoor microwave sensor uses microwave energy to form an invisible link between which two components?

The selection of the transmitter and a receiver as the correct answer highlights the primary operational principle of outdoor microwave sensors. These sensors function by emitting microwave signals, which travel through the air. When these signals encounter an object, such as an intruder, they are reflected back towards the sensor.

The transmitter generates the microwave signal that is sent out, while the receiver detects the reflected signals. If the receiver senses that the returning signal has been disrupted or altered in a way that indicates an intrusion—for example, if the return signal is less than expected due to an object blocking it—it triggers an alarm or alert. This invisible link established by the transmission and reception of microwave energy enables the system to cover large areas effectively and is useful in a variety of outdoor security applications, allowing for precise and timely detection of unauthorized entries.

Other options relate to components of an overall security system but do not accurately describe the fundamental interaction taking place in outdoor microwave sensors. The sensor and alarm generally represent the outcome of a detection event rather than the mechanism by which microwave sensors operate. Similarly, the control panel and output device, and the monitor and controller refer to broader elements of security system architecture rather than the specific functioning of microwave sensors. Hence, the focus on the transmitter and receiver emphasizes