unarm it using the key fob, if you remove the key for a certain time the immobilizer automatically kicks in but not the horn.hence if open the door the alarm don't go off but the flashing light comes on solid if you now stand outside the vehicle and arm using the key fob the red light flashes quickly while the timer is setting then settles to a steady pitch if you now open the door without killing the alarm you will have the HORN operate this time
TIP
if red light flashing car will NOT START disarm using fob if this don't work check /change the battery in the fob
wirecutterman, March 2008