So I got the siren fault warning and UEM-0004 (Siren Communication Fault) via DICE in our 2005 XC70. The car locks normally and the lights blink in the usual way, and I don't hear the siren going off. Does this still mean I need to replace the siren behind the wheel well? I've read elsewhere that the UEM computer is in the rear view mirror, and I also get code UEM-0080 Rain sensor Signal missing. The rain sensor had been working, but the auto dim function of the mirror never has (we've had the car for about three years now). Dome lights seem to work normally, too.
Where do I go from here? Do I need to worry about the siren suddenly going off while we're out shopping? Should I be shopping for a new rear-view mirror?
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-- '96 850T at about 240K, 2005 XC70 at 100K, 1999 V70 at 200K; gone but not forgotten '97 850T5, '83 244 DL, '81 245 and '64 Amazon

I just replaced my siren module with new one from FCP.Dremel with cutoff wheel to make slot & 90 degree offset FH screwdriver worked great for getting bolt out. Didn't have to have new module paired to network on 2004 V70 AWD.

I have a 2003 v70 base model. I removed the battery from the unit in the wheel well. It was leaking on the circuit board. Then just unplugged the siren unit and just left it at that. Everything still seems to work on the car I just don't have an audioable alarm anymore.
Bob v 70 & 71 1800e

no coding required, just swap in a used or new alarm .
FCP $275 new.
Or just leave disconnected, you'll just get a message every time its activated.
If you don't deal with it soon the sunroof will stop working too.

To remove the security bolt, cut a slit with a dremel cutoff disk and use a stubby screwdriver, access from the footwell.

You could test the siren by rolling the driver's window down, locking the doors, and reaching through the open window to unlock the door. Just make sure you have the key handy to start the engine and turn the alarm off if there is any noise.

Usually, when the siren module dies, the siren will not sound. Most often it is the battery pack that begins to leak all over the circuit board.

As for the UEM, if you have the skills, you could probably find the fault by checking the circuit board and repairing the circuits. Buying a used one is problematic, as you would need to update the software and the Chinese code reader will not allow you to get software from Sweden.

XeMODex.com will transfer software from your UEM to a 'good condition' used UEM, for $700+...

A Volvo deal will charge you around $1200 for a brand new one!
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Keeping it running is better than buying new