What is a sensor?
A sensor is a device that can detect an analogue signal e.g. movement, chemical composition, temperature etc. We personally use sensors for touch, taste, smell, hearing and sight. The second function of a sensor as discussed here is to convert this analogue signal into an electronic signal that can be sent to a processing device, our brain or for a motor vehicle the electronic control unit (ECU). The processing device can then decide if it needs to change something to compensate for the signal it is receiving e.g. move your hand away from something that is too hot or in the case of a lambda sensor instruct a change to the fuelling system on an engine.