try this. When the alarm is going off, open the door and put the key in then turn in the unlock position. Thank should turn it off. If not then you have something wrong with the system. Under the drivers seat, the alarm module is under there so you can temporarily or permanently disable it

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6