Peugeot 206 Limited Edition Gti Hdi, Alarm?

I Have An 05 Plate Peugeot 206 Limited Edition Gti Hdi, As Standard It Comes With An Alarm And Immobiliser. My Alarm Doesn't Seem To Work And Wondered If Anyone Can Help As Im Not Sure Whether It Can Be Enabled/Disabled And This Is The Problem Or Its Just Not Working. Also Iv Been Told I can Manually Adjust The Sensitivity Of The Alarm, Again Not Sure How To Do This, Any Help Will Be Much Appreciated!! =) Thanks