This is one of those nightmarey ones that are difficult to answer without some kind of physical diagnostics or at least seeing the vehicle.
A few pointers though, the alarm systems on these have two types of trigger. The first is a perimeter trigger such as a door opening or bonnet lifting, the second is internal motion. For the door opening, it uses your interior light switches mounted in the door appertures. If one of these is faulty to a point that it is activating your alarm, I would also expect it to be flickering the interior light when switched to "doors". If not, check out the hood sensor position. ie. is it being depressed enough by the bonnet. To do this, put a thin layer of plastercine or modelling clay on the bonnet where the switch would make contact, no more than 1mm thickness. Close the bonnet and open it again to check the contact level. Also check the switch itself to see if it is secure and not moving around.
If all the above finds nothing wrong, then the problems are a little more sinister. It could be the sensitivity of the motion sensor or it could be the siren itself. The sirens have a tamper mechanism built into them. It works by them holding a charge in an internal battery, then if somebody tries to disconnect it or the main battery whilst armed, the siren goes off and stays going until either disarmed or the internal battery discharges. If you say you cannot silence it with the remote, I would imagine it to be something like this as the cause as the signal from the alarm ecu isn't getting to the siren.
Two questions. When this happens, do the indicators flash?
and
Do the indicators acknowledge the remotes buttons being pressed even though the alarm doesn't shut up?
