She clearly took a leak when she got back in the van from the back door. Readjusting the pants when she got out is the give-away. I wouldn't want to drink that either o_O
Leaving a car unlocked is unthinkable in this country, and it is something we would never forget to do. Leaving anything remotely of value visible in a locked car is also a big no no.
So car checkers are an unknown concept here, if they are at your car there are much larger intentions.
Check out the Sonoff Basic, install Tasmota as linked above. It supports a huge variety of sensors. Link up to a local MQTT server and you are good to monitor and log data in any number of home automation apps available.