This Yueton Alert Monitor Tire Pressure Cap is great for keeping an eye on vehicle’s tire pressure at just a glance. It has three indicator colors which are green, yellow, and red. When in normal mode the tire pressure transparent window is all green indicating normal pressure or proper tire inflation. When in warning mode the tire pressure is slightly lower than the proper tire inflation by about 10% or more. Then the transparent window is yellow and should be inflated shortly not a big rush but should not be ignored. When in danger mode the tire pressure is lower than the proper tire inflation by about 25% or more. Then the transparent window is all red meaning it should be inspected and inflated immediately. If tire inflation is reduced by 15%, your car will increase fuel consumption by 6% and the tire wear will double and will increase the risk danger risk by 30%. The hazard of insufficient tire pressure is the increase of fuel consumption, and it will affect braking performance. The tire pressure cap has a CCC certification. The standard tire pressure is 2.4bar or 30lbs./sq.in. there is four Alert Monitor Tire Pressure Cap per pack.