Hello, if you find the CEM inside the car, above the drivers feet, you will see some fuses. There is one fuse 8 (or F8). This is for the siren itself. Remove that fuse. If the alarm still goes off then there are bigger issues with the car. At least this should stop it from making noise until you can get it to the shop.
Again, this fuse panel is inside the car, in a box, with relays and fuses. The relays are above the fuses, on the drivers side (us models) over your feet, on the door side of the compartment. good luck.
Technician
20 Years Volvo experience, Based in Maine, Volvo certified Expert. expertvolvo.com