This ad is for a lot of four (4) OEM Mopar Dodge Dakota Ram TPMS Tire Pressure Monitor Sensors. They are brand new in the original package. Part Number: 68137699AA The tire pressure sensor is a battery powered direct sensor (meaning directly integrated with the wheel and tire) that uses a radio frequency to transmit data to the instrument cluster in the vehicle. As long as the tires are within a certain pressure range of each other, the system is set. If one or more tires loses or gains more than a certain amount of pressure (about 20 percent to 30 percent of air pressure difference between the others) it will trigger the instrument cluster panel and set off a warning indicator light or a "low tire pressure" light. Please use the pictures and part number to make sure this is the part you need for your vehicle.