Purchase this item and not happy with the results.  First set was 4 PSI off that was tested with 3 tire gauges.  Second set same.  Third set I am now 2PSI off.  Would not recommend this at the price.  Good concept but is not within mfg specs of +-1PSI.  I decided to keep it since I went to so much trouble replacing the item 3 times.

$200.00 for the set or around that which is approx.$100.00 per wheel for something to monitor my air pressure. I always check my air pressure before I take a ride, and for that much money I would expect it to fill my tire with air too if it was low. A new tire is not  much more than that depending on what kind of bike you ride. No thanks I`ll keep doing it the way that has worked for years and doesn`t cost except the time to check the pressure the old fashioned way...

Actually - I don't run the locks on my bikes. It's simply a valve stem cap - no more difficult to add air for me! And... I know what my air pressure is at all times - without an intimate encounter with the ground