In an effort to conserve battery life, these sensors enter a 'sleep-state' after a few minutes of no vehicle movement and consequently will stop transmitting data to the app. They will wake up and begin transmitting once the vehicle is underway, typically within 30 seconds. Due to variations in electronic tolerances, certain 100 psi labeled sensors are unable to resolve pressures above 90-92 psi and as a result will report 0 psi. if your tires have an operational pressure at or above 90 psi, we suggest purchasing the 150 psi labeled sensors. Up to 99 vehicles on one phone application. All Bluetooth Low Energy Devices are addressable ID & can be reconfigured in seconds on your free phone app. Sensors monitor both tire pressure & temperature. | Advanced Accessory Concepts LLC BLU Tire Pressure & Temperature Monitoring System, External 1-100psi, Set of 6