Here is a product I just found that allows you to monitor your tire pressure on your vehicle and trailer. No tools are necessary to install PressurePro and the system is simple to operate. A wireless, tire air pressure sensor (cap) simply screws onto the valve stem replacing the dust cap. The Monitor is powered by plugging into the lighter accessory in the vehicle and displays current tire pressure as well as alerting to low tire pressures with both a visual and audible warning. The sensors constantly read the tire pressure and transmit low-pressure readings immediately when they occur. When tire pressure is low, the monitor identifies the low tire position with a flashing light on that location and an audible alarm to alert to low pressure. Retail is about $490.00