What's covered in this FAQ?
1. Types of alarm problem
2. What sensers the car has
3. How to check if its the Ultrasonics
4. Aftermarket alarm fault codes
5. Part numbers for sirens and ultrasonics
6. Locking and unlocking with alarm and key fob problems
7. LED on with car running
The two types of problem alarm
Alarm + no flashing lights
Knackered siren / siren battery
Alarm with flashing lights
Knackered siren/siren battery
Problem shut sensors
Voltage drop (main battery)
Voltage drop (siren battery)
Other basic info
Alarm, sensors and what it detects
Ultrasonics = movement in car (can be disabled)
Voltage drop/tampering with main or alarm battery
First thing I'd check - Ultrasonics
If you have a hyperactive alarm then try setting it with the ULTRASONICS disabled. If it stops going off at random then chances are your ultrasonics are knackered.
To test if they're working then you can set the alarm with the window open, then wave your hand round inside after a minute and it should trigger the alarm, if not your ultrasonics are also knackered (but in a different way)!
The way for setting the alarm with no ultrasonics is set out at post # below.
The part number for the sensers is at post 3 below.