I keep mine pretty full, have never seen a low fluid light. It's specially important to top it off before having service, I've had dealer monkeys top it off with plain water which decreases it's effectiveness on removing road film besides making it more susceptible to freezing.
I just moved to an area where it freezes......it was 14º for several nights and didn't get above freezing for three days. Being from deep south Texas I never thought about it until my windshield squirters froze up. Auto Zone had their brand on sale 2 gallons/$5.00. Good to 0ºF.
I add a 1/2 a bottle of this to my purple Splash brand -25 below stuff to the holding tank in my car. Splash brand that is sold locally here, because the manufacture is here in Minneapolis. I no longer get frozen nozzles that kill any cleaning of your windows.