Iuhan&reg; New 4PC Auto Tire Pressure Monitor Valve Stem Caps Sensor Indicator Alert Round Style: 36PSI3. 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. Simply look at the color to know if your tire is low or normal Package Content: 4PC Auto Tire Pressure Monitor Valve Stem Caps Sensor Indicator Alert(with retail package).