old school observation.... tire whacker

I don't personally know anyone that can tell the PSI by thumping the tires, but I know personally that I can tell when one is different sounding. I check my tire pressure with a good quality gauge (and have a backup gauge if I doubt the first one) periodically, but sometimes on a trip longer than a few hours, I just want to make sure I don't have one going low... I plan on getting the infrared laser thermometer and will probably just use that. A tire that is low will run hotter (no, I don't know how much yet) so I suspect I would see a temp difference on a low tire. Walk around at rest stops is a good idea, it is nice to stretch legs and make sure things look okay. If I get trouble from LEO for tire thumper, I have worse problems to deal with..