RealWheels RW-PPK-0402 Air Guard Tire Pressure Monitor with Security Locking System - 4-Pack is designed to be the easiest tire pressure monitoring system to install, calibrate and recalibrate. For use on tires with pressure ranges of 10 to 200-pounds. Red strobe flashes if the pressure has dropped between 5 to 10-PSI. Includes anti theft security locking system. It promotes improved fuel economy, safety and longer tire life.