Sorry just saw your question today? It would seem like you could have 2 separate problems here? What you should do is call Volvo to see if they are participating in the Volvo service for life program.
If they are then they should give you a free scan and some basic checks. For the alarm fault, if you have a sunroof and it intermttantly does not work then the siren is faulty. To replace it you would need to have the new siren reconfigured to the vehicle for it to work properly. For the SRS fault I would need some fault codes also to get an idea as to what the problem could be? If you take it in to Volvo you should get at least a print out of all the fault codes stored. You can post your codes from there. The fault could be something from a faulty instument cluster, SRS control module, the contact reel or air bags, maybe a faulty impact sensor, or something if there is multiple network commjunication faults a bad central electronic module or an issue with the CANBus wires? So as you can see it is very hard to diagnose a light online without at least posting some sort of fault code on here to get an idea? So check out your nearest dealership and let us know what happens or give us the fault codes.