If this is anything like my old Honda Civic, the alarm siren has "backup" batteries in it. When they expire - which I expect they have on a 1997 car, they can cause all sorts of havoc with the alarm, and start to drain the main car battery too.
I'd see if you can find a fuse for the alarm siren to remove or and unplug the siren completely and see if your problem goes away.
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2017 V60 D4 Geartronic
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