If you have your original wheels stored near your car then your light generally wont come on if you drive short distances. I bought some 17s and never installed the TPMS. The light only comes on after driving around 15 or 16 miles of my comute to work. If I am just driving around town, then it won't come on. I have my stock steelies stored next to my car and after a night of being in the garage the light goes off.
2012 Focus SFE with a sunroof and SYNC: Currently 34.2MPG
Dual Clutch Transmission = Junk.