Last summer I had added an aftermarket tire pressure monitoring system. I selected a very reasonably priced add-on system I found on Amazon (Favoto TPMS Tire Pressure Monitoring System Wireless Solar Power Installed on Window Pane with 4 External Sensors LCD Real-Time Display 4 Tires' Pressure&Temperature 22-99 PSI https://a.co/d/8UdBOuN
Lower priced models like this have external sensors that mount on the tire stems. These present a few challenges. Each sensor is specific to wheel position (RF, RR, LF, LR). So if you rotate tires you need to reposition the sensors to the correct tire. External sensors usually have to be removed to adjust tire pressure. It is not all that difficult, although when I asked the dealership to rotate the tires and swap the sensors their shop geniuses could not figure out how to do it, despite fairly clear instructions. Simple solution is remove them when you go in for any tire related service
I like that this model's display is solar powered. It mounts on the windshield interior and charges during the day. The sensors have button type batteries that last years. The display is easily readable in daylight and not too bright at night.
While the system allows for alarm set points (beep if tire pressure or temperature goes outside set points), the set points apply to all 4 wheels. My RoadTrek has 80psi rear and 55psi front, I set for the 80psi. If I replace the system I would look for one that allows different set points.
So the system proved its worth when it alerted me to a front tire that was losing pressure. I quickly found a tire dealer on my route that had 2 in stock.
While they had the RoadTrek I asked them to check the spare. Although it had lots of tread, it turned out it was THE ORIGINAL spare from 2006. I had them replace it with the non-leaking tire off the front. The original spare would not have likely lasted very long in use and the one I used was much newer with plenty of tread left.