G'Day ,
Each rim has a sensor in it that talks to a system in the car( via bluetooth ?)
Car system , as part of start up , checks with each sensor to ensure that it's working and the amount of pressure its holding. As you drive, they talk at regular times and if a difference is noticed a warning comes up on the dash indicating each pressure and will continue to show warning if pressure continues to drop.
Our Kona has gone off once showing a difference of 1 psi.
( I said -"really! , 1 psi !, )