Your can impress your friend at Toyota by telling him how the TPMS systems work...
Toyota made two kinds of systems - "direct" and "indirect" measurement. They tried the "indirect" first, which may be what your friend is calling the first gen. Indirect TPMS works by using the anti-lock brake computer to measure the speed of the rotation of the wheels. A significant difference in one relative to the other three is a good indication that one tire is low on air. So that didn't work on PSI, but rather by noticing that one is different from the others. Somtimes that means that one tire had to be as much as 15 PSI lower than the others, but it varies based on driving speed and other factors. That system had its flaws, including false alarms in certain driving conditions and also the inability to detect if all 4 tires were lower than they should be. If someone never checked the tires and all 4 lost air naturally over time, the computer wouldn't know.
I believe Toyota has moved all models to the "direct" system, which is on the 2004+ 4Runner. Now there are sensors inside all 5 tires (4 + the spare), and the sensors use little radios to transmit actual pressure readings to a central computer. The threshold for when the system turns on the idiot light varies by Toyota model. The 4Runner is hard-coded at about 27 psi, but other models have slightly different values, and some models even have a calibration button that allows you to set the level based on the current pressure in the tires. The Land Cruiser has an option for a second set of sensors for "winter wheels" versus "summer wheels". The direct system has a couple of drawbacks, too. The sensors use batteries, giving them a lifespan of about 5 years, and they're expensive! The sensors are part of the valve stem, which means the guy replacing your tires has to be careful when mounting and dismounting them. Finally, because the system is more complex than the indirect system, something could fail, such as a bad sensor, and make the idiot light flash incessantly.
There are a lot of threads about the merits of the system on the 4Runner, as well as how the active TPMS works in more detail. A search for "TPMS" will pull them all up.
