how can i stop my burgular alarm from chiming?

Hi wonder if anyone can help, we have a Accenta G3 Mini burgular alarm system and for the last 4 week we have been having problems with the door chime going off even when the door is closed . The noise the chime makes when the outer door is opened is a double chime and this noise is a single chime. Has anyone any idea what i can do to resolve the problem its driving me mad . Thanks..