It is detectable on arrival.
It does depend on your use case and how quickly you want it to be detected.
Mine is detected within 30 second of arrival (coming in to range of my wifi). All of my car stats get updated whenever the car gets back home.
I could make that check more frequently and get that down to 10 seconds.
As it is just wifi, you could also just check if your router has a connection to that IP (of your router supports that in HA).
Or you could just try to open the web page. If you get a 200 OK then you know the car is back.
Now, when the car is off you can tell the WiCAN to not go to sleep. So you could have constant details of the car being present. That will drain your 12v battery some though. No worries for an EV that auto-tops up the 12v battery but a problem for an ICE car.
The device’s sleep mode is still pretty good for tracking presence though. It wakes up every hour and does some checks. That will show as present on the network. It will also send an mqtt message if certain conditions are met.
You could ask for the developer to add a shorter sleep period for your use case also (like 15 mins) or do a custom esp32 firmware yourself.
I think you can make it work pretty well. A very nifty little device.