The low coolant level warning light uses a sensor in the cooling system to monitor the coolant level. The sensor is typically located in the coolant reservoir, radiator, or engine block.

I'm not sure what the oil level sensor was, but it was bolted onto the side of the oil pan, so it can't have been terribly complex. Why don't more vehicles have these devices?

Answer:There's no switch in the radiator. The low coolant level sensor in the coolant expansion tank is intended to be the sole signal that activates the message at the Vehicle Information Center ...