2008 Toyota Highlander Tires Complaints How Do Tire Pressure Monitors Work?

How do tire pressure monitors work? - 2008 toyota highlander tires complaints

I have a 2008 Toyota Highlander Hybrid and tire pressure monitors. I wonder how well this works. What is measured by the pressure, as transmitted to the computer of the car?
(I guess it works the same way in most (all?) Did the car, so I'm posting this in the general category, not in the Toyota category.)