A smart home is only as smart as the information that it has access to.
A modern car has so many sensors installed that, as long as you have the correct tool, the car can tell you what is wrong and how to fix the problem! You've seen them, tire pressure sensors, seat belt sensors, gas tank sensors (to tell you how much gas is left in the tank), door open sensors, oil pressure sensors, temperature sensors and on and on and on. Those are just the ones that you can see! There are hundreds of sensors throughout the various systems of a car today. All of these sensors are talking to a central computer that can put the car in "limp" mode to limit major damage but still get you home or at the very least a safe place or a mechanic.
A smart home uses sensors in the same way.