As title states, this message has come on my dash the last few days, along with DTC for UEM0004, which is Upper Electronic Module - Siren.

So a quick and simple test:

Open drivers door window.
Close door and lock vehicle.
Wait until deadlocks activate (you'll hear a quiet secondary lock engage in the door)
Reach into the car and pull the bonnet release.

The alarm should immediately go off, as it did in my case, Indicators should all be flashing. If you cannot hear the siren but your indicators are flashing then the Siren needs replacing.
Unlock car to disable alarm and then note the dash LED will be blinking quickly to tell you the alarm was triggered.

I have now cleared DTC's and ordered a new alarm siren from Volvo which I'll collect tomorrow and fit.

Price is £166 retail.

Easy fix to: Jack car on right side front. Remove wheel. Pull down wheel arch liner to access alarm siren just above washer bottle. No software required, just remove old unit and fit new.