Tire-pressure sensors the car's radio has heard while driving around.
Since about 2008, new cars sold in the US have had a pressure sensor in each tire that
sends out a short radio packet (its ID, pressure, and usually the temperature) on either 315 or 433 MHz.
A cheap software-defined radio running rtl_433 can decode them, so the car picks them up
from whatever is driving (or parked) nearby. I only publish counts and histograms here, so sensor IDs only stay in
private logs.
Pressure readings decoded, in PSI (one sensor can be heard more than once). Most passenger cars need about 32 to 35 PSI cold, so the bars below 30 are probably low tires. Trucks, spares, and odd decoding errors land in here too, so I read the low end pretty loosely.
The rtl_433 decoder that matched each sensor.
These actually name the radio protocol, not the make of the car. A handful of suppliers build sensors for many, many brands, which is
how "Renault" and "Abarth" end up on Texas roads. Rare ones are just pooled into Other so that no
single unusual car stands out.
US-market cars mostly use 315 MHz, while imports use 433 MHz. The receiver now hops between the two with equal listening time, but my earlier captures didn't log which frequency a packet came in on, so most sensors so far fall under not recorded.