In the broadest definition, a sensor is an object whose purpose is to detect events or changes in its environment, and then provide a corresponding output. A sensor is a type of transducer; sensors may provide various types of output, but typically use electrical or optical signals. For example, a thermocouple generates a known voltage (the output) in response to its temperature (the environment) There are many kinds of sensors to help driving, safety and parking and so on. (Airbag, Automatic transmission speed, Camshaft position, Coolant temperature, Crankshaft position, Fuel level, Fuel Pressure, Knock, Light, Oil level, Oil pressure, O2 sensor, Mass flow sensor etc.)