Some of us do not carry a spare tire. Instead, a tire puncture repair kit, 12V air pump, AAA card and cell phone can come in handy.
Recently I installed an aftermarket tire pressure monitoring system,
http://www.amazon.com/gp/product/B002DYH586/ref=oh_details_o05_s00_i00This system seems to have gotten the best reviews and the price is reasonable.
Installation is quite simple, but the tires have to be dismounted to do it so I waited until it was time to rotate.
The display is the size of a credit card and sits on the tranny hump. Read out for each tire is in real time for pressure and temp. Scales can be psi, kPa, or bar, and farenheit or celcius. I have checked the pressures with my sliding tester and the read outs are quite accurate. Visual and audible alarms for over/under pressures and/or temps. come pre-programmed, but can be adjusted. There is also a function to accommodate for when tires are rotated so that the receiver knows which tire is where.
Ther car's battery voltage is monitored as well.
What sold me on a TPMS were the anecdotal reports of drivers being alerted to a pressure loss with enough time to slow down and pull over. Obviously, it won't help in case of a massive blowout.
