Security system goes off when door open

[bn.ladoremi@xxxxxxxxx]

My house has a Vista-20P for more than 6 years. A couple of days ago,
the LO BAT showed up on the keypad. After research on this forum, I
was able to replace the battery. The old battery was UltraTech UT1240
(12V4Ah). The new one is  Werker WKA12-5F (12V5Ah). The guy at the
store told me that 5Ah is better and shouldn't cause any problem. I
installed the battery yesterday without any problem. Today, when I
open the back door, the alarm goes off (both siren and keypad) even it
is not armed. The system works normally with all other zones,
including other doors.

Could it be the new battery? Thanks for any help.