4 PCS Tire Pressure Monitor Stem Caps,2.4Bar 36PSI Car Tire Pressure Monitor Sensor Indicator with 3-Color Eye Alert,Universal Stem Caps for Cars (Gold)

I was curious too so I looked them up.https://www.walmart.com/ip/4-PCS-Tire-Pressure-Monitor-Valve-Stem-Caps-2-4Bar-36PSI-Car-Sensor-Indicator-3-Color-Eye-Alert-Universal-Caps-Cars-Gold/19915673888 Set to 36 PSI, yellow is 10% low, red is 25% low. It isn't terrible if, say, you have a new driver daughter who doesn't pay attention to this stuff. What I'm more concerned about is how well these little Chinese things seal. Probably let more air out, but this way you'll know!