Originally Posted by Kabigon
There is no mechanism to detect a low coolant level directly (i.e. it could only be detected by a high coolant temperature).
It would be nice to have a coolant level alarm but I'd guess the engine coolant system is a bunch tougher to sensorize than washer fluid. First, it's hot. Then you have the water pump causing the fluid to be quite turbulent. Finally, it's pressurized so whatever sensor would need to be fully enclosed.
Should still be doable, but certainly not as easy as washer fluid.
A similar thing with motor and transmission oil levels.