No, you can’t just leave the camera when it is not connected to WiFi. Our Wyze Cam in the auto shuts off after 1,5 hours without WiFi when we motor away from our building with WiFi connection, recording to µSD card ceases after 1,5 hours automatically, then resumes automatically once we come back into range of the WiFi. You will require a portable WiFi router such as listed in this post/link below. We have not tested this solution in our auto yet. However, in your situation you can probably bridge your own router with one of these and you can place the portable router in your auto for additional security. The camera can then be placed inside or outside the vehicle as you choose. Anywhere in range of the portable WiFi router/bridge of course.
Hope this helps,
Thanx,
73’
Tuna