Could be anything but here are some thoughts..........
Either cripple it all together or get it fixed.
Carefully look at all wires that run between the car itself and the doors. Make sure the trunk switch and the hood switch (and there wires) are in good shape. If there are door ajar switches visible, make sure they seem to operate smoothly. Does the car have any water leaks? That can cause complications as well.
You may need to pay a dealer to do the work you need as a specific scan tool will be needed to look at the various signals and the module that initiates the blowing of the horn/flashing of the lights.
If you have no interest in getting fixed, I would think that for about 1 hour of labor (100 bucks) they could either cripple it electronically or they could cut a single "magic wire" that will keep the system from being armed.
If you want to get it fixed, be very specific about the conditions and circumstances that surround each "event".
I am assuming this is a factory system.
Sorry about the problem. I know it is frustrating.