Car Alarms: Car alarm going off, valet mode, dash area

Question
Help! The alarm on our Volvo S40 keeps going off.  It had been to a garage to sort out a power-steering problem and on its return the siren started but no lights flashed.  No pushing of fob buttons or opening doors would stop it and it continued intermittently for several minutes.  12 hours later it started again and (for the sake of harmony with the neighbours) my husband disconnected the battery.  The garage had it back.  Checked the bonnet sensor and all other bits and kept an eye on it for the next 24 hours.  Nothing.  We had it back yesterday and it was fine.  Today, close to the same time, it's started up again.  There's no mobile phone left in there and it's on a quiet road with little traffic - there was nothing going past when it started up again. The garage doesn't know what to do next apart from disconnecting the siren. Can you help?  Please...

Answer
Hmmm, from your description,
it seems the system is in long tamper mode, and needs
to be reset.

Right, Ok, try this.
Put the key in the ignition, and turn forward
all the way just before cranking. Then within
5 seconds, press and hold in the valet/overide
button, found under the dash area, usually to the left
of the leg, drilled into a plactic panel.
Might even be part of an on glass antenna
in the widshield if it's a remote starter,
until the installed LED (the blinking light)
in your dash area goes off, and the siren chirps twice.
(Your valet switch might be the toggle (on/off) type.
in this case, key on, flip switch in oposite direction,
key off.)

This should reset the alarm and allow you to
go on your way.

Just Repeat these steps to place it
back to valet mode.

That should do it.

Good luck.

ALARMTEK