Hi,
Assuming they haven't changed it on the 2001 version I'll tell you how I switch off the alarm on my 1997 Marea HLX 20V saloon.
As well as the blue ignition keys have you got a small key about an inch long, the blade of the key opens out to a kind of cup shape like the letter O if you were looking down on the key when it was standing on end.
Assuming you have that, the next thing is locate the fuses, on my 97 Marea they are behind a panel by the driver's door under the steering wheel. Should have two screws holding it in. Remove this panel, you can see the fuses, you should also be able to see a key barrel covered by a black plastic cover. Take the cover off, insert the little key and turn (I think anticlockwise) and that will completely switch the alarm system off. The remote central locking still works when I do this on my Marea.
Its all in your user manual if you still have it.