The battery on my 2005 Chevy Classic (AKA Malibu) went dead so I had it replaced but the anti-theft “Passlock” circuit got tripped. What a royal pain! All my neighbors now hate me because the alarm just kept screaming so I disconnected the ground wire on the horn - big mistake because the anti-theft was then convinced someone was stealing the car.
To reset the alarm you have to leave the key in the “on” position for at least 10 minutes listening to that damn alarm the whole time. To resolve the issue I filled the alarm horn with caulking then went through the reset procedure without having my ear drums bleed.
What a dumb mess, G.M.