reseting my car alarm

[theolcia]

just bought a used motor 97 vauxhall everything is fine untill i press unlock button on the alarm fob as soon as i open the door the alarm goes off and i need to turn it off tried most things even standing on one leg and whistling dixie but cant get the thing to work proper car locks fine its only when i open the door after unlocking it alarm goes off please help me if only to stop the people on my street from stringing me up in the morning.