When the driver leaves the car, detect if a passenger is in the vehicle, perhaps with the seat belt sensor, and leave the HVAC and audio active.
The option should send a warning to the app if HVAC has been active for more than 30 minutes.
This is a hidden safety feature, as if you forget you baby, the car will provide a safe temperature until you return and is also useful for when you want to sleep in the car or are at a Drive In.
Moderator – If the driver is gone, anyone taping the screen will bring the HVAC and radio back on. In many places in the USA, it is illegal to leave a child in the car unattended, even if the car is running. Also, it is not recommended to use a child seat in the front seat, and there are no sensors in the rear seats (although that could be part of the feature!).