Some versions of the 453 have interior sensors for the alarm.
The coupe has ultrasonic sensors and the cabrio has interior protection sensors.

It looks like these can be deactivated in DDT4All.

Interior Proximity Alarm Deactivation

Start DDT4All and connect to the car.

In the 2nd box on the left, select [BCM].



In the 3rd box, select Alarm Perimetric and then Alarm Perimetric - Configuration.



Click on Einstein's face to enter expert mode.



In the main window, look for Perimetric_Alarm_CF.



Change the true to false and click send.
The interior sensors should now be disabled.