What is happening to tsikot??? I had just replied with a loooooong explanation on auto start feature and it does not get posted?
Anyway, (*sigh*)... back to the topic at hand.
Assuming that you have parked your vehicle, placed in neutral position or "P" in auto tranny units and activated your alarm. Different kinds of alarms have different kinds of features and buttons for activating the auto start function. Press that button once you hear the engine crank and running. While some other brands have the auto delay which will turn your A/C on after the engine has been running for 5 minutes. While some other brands will set your A/C on as the same time the engine is running. Some auto start features have 15 minute idle cut off time while others will remain at idle until you switch the engine off manually.
Now, when entering back to the vehicle, deactivate the alarm or unlock the doors using the remote switch as you would normally do. Keyhole acess is a no-no, your vehicle's alarm is still in active mode and the engine will shut and alarm horn will go off as if someone is attempting to steal your car.
Once you have opened the doors and sat in. Place the key to ON position to automatically switch off the protect mode from your alarm and drive off as you would start an ordinary car. No need to crank up the engine again, while the engine is at idle.