Automatic tire-pressure checks.(Up front: news/trends/advice)

Some new cars and trucks have begun offering tire-pressure monitoring systems. But these important new safety features aren't limited to new vehicles. We tested four effective systems that can be mounted in any vehicle.

How do they work? Sensors mounted inside the wheel transmit a signal to a receiver and alarm inside the car. Direct systems like these are superior to indirect systems, which use wheel speed to gauge air loss.

All the systems worked well and reliably They alerted us to a low-pressure status in one or more tires and correctly identified the deflated tire in less than one mile of travel.

We tried two versions of the SmarTire Gen II: a basic one with a flashing light for a warning, and one with a display ($50 extra) that gives tire pressure and temperature.

How easy to install? We recommend professional installation. Most sensors mount inside the tire, on the wheel rim, so the tire has to be removed from the wheel. The Intellivalve puts sensors in the valve stem, which entails a partial tire removal. Installation should take about an hour for most systems. TireSafe ...