Most people don't carry a tire-pressure gauge in their car. A new federal study shows that underinflated tires triple the risk of an accident. Low tires affect braking, accelerating, cornering and fuel economy.

People might be overconfident, considering that almost everyone has a tire-pressure-monito​ring system in their car, as long as it's less than five years old. The government mandated the technology in 2005, but it wasn't required until September 2007. Unfortunately, those systems only tell the driver when the tire is low. Most don't say how low, or let the driver know whether he's overfilled the tire.

Nissan's system uses the car's four-way flashers to let the driver know air is coming in. Once the tire is full, the horn beeps once. If the driver puts in too much air, the lights blink faster and the horn beeps three times. When the tire is deflated to a proper level, the horn chirps one more time.

“It's one of those simple slap-your-forehead moments, as to why someone has not thought of it before,” said Vishnu Jayamohan of Nissan product planning and advanced strategy.