Photoelectric switch (photoelectric sensor) is the abbreviation of photoelectric proximity switch. It uses the obstruction or reflection of the light beam by the detected object, and connects the circuit through a synchronous circuit to detect the presence or absence of the object. Objects are not limited to metals, and all objects that can reflect light (or obstruct light) can be detected. The photoelectric switch converts the input current into an optical signal at the transmitter and emits it. The receiver then detects the target object based on the strength or presence of the received light. The common photoelectric switch smoke alarm in security systems is often used in industry to count the number of movements of robotic arms.