Our 2002 volvo s60 alarm (sounds like a bird half-chirping) will go off intermittently. Also parking lights flash when it goes off sometimes. We have 3 differrent remotes at tried locking with all 3. Alarm went off today when using key to lock door. Usually alarm quits when un-locking car but today it sounded off for a couple of minutes of driving.

SOURCE: volvo s60-2.4 D5 2001

Its most likely your siren module.

It is located in the right fender well just behind the wheel liner.

Remove the R/F wheel, remove the torx 25 screws, pull the liner to the rear and you can see it right there above the liner.

To remove the siren module...it uses a sheer bolt, which unfortunately you'd need to either drill it out, or use a dremel to slice a slot to get a screw driver in to remove the sheer bolt.

SOURCE: the alarm is on

Try  closing all the doors.  Using the key in the drivers side door turn the key to lock all doors (i think it's to the right) then turn the key twice the other direction; unlocking all the doors and the alarm should stop.  This just happened to me tonight.

SOURCE: volvo s80 alarm

Have the codes read out for the vehicle. It is likely that the siren for the alarm is causing the false alarm. If the siren is bad, there will be a code set in the central electrical module. (CEM)

SOURCE: Alarm haywire, can't override anti-theft system or turn on car

The Alarm on my Mercedes ML320 sounded every night, then it started doing it more often, Showed it to the dealer he says it's the 'Tow Sensor', that needs to be repaced. $700, down the drain. I have already started hating this car, it eats $500-600, every 6 months...

SOURCE: auto door locks 200 volvo S70

You may have a bad master door swith assembly or more fuses out.