Steve,
The Keyless vehicle security system manual is seperate from the vehicle manual.
According to page 10 of the manual, what you need to do is: insert the key into the ignition switch and turn it "ON-ACC-ON" to disable an alarm.
Page 10 also indicates that the alarm will sound when power in the vehicle is lost, then restored. So what you've been experiencing is perfectly normal.
I'll try to scan the manual but it probably won't happen till late next week.