I have aftermarket TPMS in my setup after having one tire go flat on me. When you're running a LP setup, air just goes goes out very quick. The alert does a visual large red light lights up and a audible tone as well.

Mine *smartire* also does give e real time pressure readings. It's nice only needing to need the air gauge whenever I need to do a fillup. No more checking of tire pressure...

Then again, I'm just sensative to alignment and can also feel when the pressure on one tire.