Passive sensors are devices that detect and measure energy naturally emitted or reflected from objects, rather than generating their own signals. They rely on external sources of energy, such as sunlight or thermal radiation, to gather information about the environment. Common examples include cameras that capture visible light and infrared sensors that detect heat. These sensors are widely used in various applications, including remote sensing for environmental monitoring and astronomy for studying celestial bodies. Because they do not emit energy, passive sensors are often less intrusive and can provide valuable data without altering the conditions of the area being observed.