Tire Pressure Monitor Valve Stem Cap Sensor Indicator 3 Color EyeMaterial: Chromed Metal. Round Style: 36PSI Fit on any standard size existing tire valve stem. Visually alerts you when the tire pressure is low to help avoid premature tire wear or blowouts from under-inflated tires. Green shows that tire pressure is normal. Yellow shows that the pressure is down about 5 pounds. Red alerts you that the pressure is down by at least 10 pounds. Determine the correct tire pressure for your tires. Inflate tire to correct pressure. Install This new pressure cap tight. Simply look at the color to know if your tire is low or normal.