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...
I have a set of 4 of these caps that I never installed if anyone wants them. Suposidly they will eventually leak and cause a flat and I didn't want the headache of worrying about my solution causing the problem that it was there to solve. If you search for this topic you will find the previous discussion on this subject.