The first thing I would do is check the battery (and the battery in you fob) and reset the alarm (check the hay man for this) (the alarm should always be turned off before removing the battery) then check the alternator to see if it working right or if the belt is lose, the alarm has current sensing (this is where, if the battery goes low then it goes off (about 10v or lower). Any problem with the alarm then you must take it to the pug dealer as they can test it and if needed reprogram or replace it, I would also get your keys reprogrammed along with the immobilizer.
The reason the CC alarm went off when the 206 key was pressed is probably the alarm on the CC was picking up the signal and thought that someone was trying to find its disarming signal so they could pinch it (so it was like a warning).
Hay manual says to turn it off you turn key then press and hold the internal sensor switch until the alarm light flashes then switch off.
To turn back on just use the fob to deadlock the car.
hope this works for you.
steve
(But I did under stand it)