In light of all of the TPMS comments being posted, I thought I'd mention this hack. Buying a lightly optioned used 997S, I was really disappointed that it didn't have TPMS. Or rather, that it didn't have some way of monitoring tire pressures. Given the low profile tires, it seems like paying attention to tire pressure on this car is particularly important. Adding TPMS is not possible (I'm told) and it's not that impressive a piece anyway.
So two years ago I bought this: http://www.tpms.ca/PTSD4info.html - a very nicely designed real-time pressure monitoring system. No senders to be installed under the tire, comprehensive data, seemingly quite accurate. Tradeoffs are that the senders can be easily damaged by curbs or evil doers, and theorically the tires should be rebalanced due to the added weight of the sender. But so far, no problems.
I used to mount the received with velcro 'under' the e-brake handle (on the banana as it's referred), but when I installed an alcantara center console, I was a bit stuck. I might go for a more subtle and permanent mount in time, and I can see from the photos that it needs a bit of adjusting, but for now it's 'wart helper'.
Photos:

 

Cool system, does it have a low point with a warning?

 

Do the sensors depress the valve stem to access the air pressure?

 

I have to double check, but I believe so. Definitely have high-pressure warning and ID's the tire in question as well as an audible tone. It demonstrates just how widely TP's vary with temperature and driving characteristics.

And yes, it does depress the valve stems for the reading. I was very concerned about leakage with this design, but they are absolutely air tight (so to speak). I go weeks and weeks (and weeks) before having to top off.