A photoelectric sensor is a device that detects the presence or absence of an object by using light. It emits a beam of light, usually infrared, and measures the amount of light that is reflected back. When an object interrupts the beam, the sensor triggers a response, such as turning on a light or activating a machine. These sensors are commonly used in various applications, including industrial automation, security systems, and automated doors. They are valued for their reliability and ability to work in different environments, making them essential in modern technology.