http://www.ebay.com/itm/4Pc-Car-Auto-Tire-Pressure-Monitor-Tire-Gage-Alert-Sensor-Indicator-Valve-Cap-xp/272092144510?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3Df29cf121b84e4f2fb584e9615308947a%26pid%3D100338%26rk%3D7%26rkt%3D12%26sd%3D161499479655
You still have to crawl under the car to check it... but these will tell you if you have to add air.
Tire pressure should be checked when the tires are cold before a drive. If you have one of those portable air tanks, you can more easily check and add air if needed.
