I've been running #rtl_433 for a few days now, logging all the data, just to see what else I can read, and besides THREE weather stations, I've also found a couple of "TPMS" devices - Tire-pressure monitoring systems. These sensors have been mandatory in all new cars for almost 10 years now, and as it turns out they use the same 433MHz frequency as all these other systems.
Meaning, I can listen to my car's tires reporting their pressure every ~2 minutes, and when the transmissions stop, the car is no longer home!
If this works reliably will depend on your car, as the reporting times change drasically between brands. Some tires seem to have a standby mode that'll report only very spordically when the car's parked, but it seems I got lucky.