IR sensors deliver digital, analogue outputs

What is a sensor?
A device that receives and responds to a stimulus or signal. Sensors measure real-world conditions, such as heat or light, and then convert this condition into an analogue or digital representation.

What is IR radiation?
Infrared (IR) radiation is an electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves (between 750nm and 1mm). Applications include target acquisition and tracking by the military, remote temperature sensing, short-ranged wireless communication, spectroscopy, and weather forecasting.

What does analogue mean?
A continuously varying signal. For example, if an analogue signal's range is from 0V to 5V, the signal can assume any voltage within that range such as 1.2, 2.4, or 4.7V. Microprocessors and microcontrollers usually cannot process analogue signals directly and require conversion by an A/D converter before they can process the signal.