A motion sensor is a device that detects movement in a specific area. It uses various technologies, such as infrared or ultrasonic waves, to sense changes in the environment. When motion is detected, the sensor can trigger an action, like turning on lights or sending an alert. These sensors are commonly used in security systems, automatic lighting, and smart home devices. They help improve safety and energy efficiency by ensuring that lights are only on when needed. Motion sensors can be found in places like homes, offices, and public spaces to enhance convenience and security.