Tire pressure monitoring (TPM) is one of your basic self-diagnosing systems. In the simplest (read: cheapest) TPM systems, the car will tell you when one of your tires is feeling a little flabby. Not how flabby, or specifically which tire might be having a low-self-esteem day. That's up to you to figure out. Lucky for you, you've only got four choices.
Your more lah-dee-da luxury cars give you much more information. They'll tell you which tire is low and by how much. They'll even draw you a little diagram in the center console screen or right in front of your face in the dashboard. And they'll blink and beep and turn the little diagram an angry red if things get dire.
Your automotive robot overlords are very particular about their continued ability to roll along the road. They're also quite vain. No flabby tires allowed.