Unless a tire is punctured, it only loses air slowly over time, but not enough you'd really notice looking at them, but still enough that it's bad for tire wear. It's a nice reminder to me I need to add air to the tires.

The car's dashboard display also shows the tire pressures, but:

a) My wife, for whatever reason, seems blind to anything the car shows her on the dashboard. :-(

b) She'd have to put the dashboard to the screen which shows tire pressure. The TPMS doesn't alert till pressure is quite low. They are supposed to be 36 PSI. The TPMS won't alert till they are below 25 PSI or some such.