I have a 2019 GMC Sierra AT4. The other day I had the truck running while filling up my tires with air (about 5-7 psi below recommended) and noticed that as i was filling the indicator at the corner I was at started blinking then the horn chirped. So I stopped filling the tire and checked the pressure, it was right on! Then went to each tire on the truck it did the exact same thing! No need for tire gauge when filling up our tires, just keep your truck running and it will honk the horn when the tire pressure has reached the proper inflation. Amazing technology!