Mark E
Member
A lowly Holden Commodore beeps the horn if you open and then close the doors with a key fob still inside the car, no use of special sensors or apps.
That's because the holden door handles stick out with a button on them. The GM implementation is nice and simple and also has the advantage of being able to just unlock the drivers door when opening, or all doors if you double click on the button. The downside is that the handles stick out.