Alarm of Lights Light Fiesta Max 2006

When I forget the lights on and I open the car door, the alarm never sounds, but if I stay inside it sometimes, or if not when I return and it already spent a long time it can also be that I sound, as I do to sound before getting out of the car and not when I return?
Looking at some electrical circuit I saw that there was a buzzer and a microprocessor.
Someone can guide me about this fault please.
Thank you very much to everyone.

Hello, I suppose you mean the war warrar, in the body, (driver side) there is surely a micro-interrupor between the door and the fence, which is surely lazy or make their connections bad contact, disassemble and literate them and return it to squeeze, check that clicking it by hand with light light does not sound and if you release, if