Sometimes it is necessary to disable the alarm system when it malfunctions and the horn will not stop blowing. Here are instructions on how to do that.
There is an in-line fuse above the parking brake pump pedal, (FUSE A in the photo below).
It is a yellow 20 amp blade type. Removing that fuse will disable your alarm. The remote entry system will still work.
The fuse is not easy to get to.
Thanks to Richard_D, member of the Reatta forums, for this information.