Tire pressure

#1

How on earth does the tire pressure indicator on the dashboard know the tires are low?

#2

Either by the ABS system monitoring a sudden change in the rolling circumference of one tire compared to the others, or by a actual pressure sensors in the wheel.

#3

Are you guessing one or the other or are both methods used?

#4

Are you guessing one or the other or are both methods used?

Both methods are used depending on the make model and year.