srand

Hi all, I'm new to this forum and I was really happy to find it. Hopefully, someone can help me out. I have a '98 Outback. The anti-theft system kicks on for no reason. I'ts happened when I unlocked the door (using the key) and again when I went to start the car. This has happened 3 times in the last 6 months. When it does happen, I can't start the car. The only way to stop the blaring noise is to disconnect the battery. Does anyone have an idea of what could be wrong? Or...can anyone tell me how to disable the system? Thanks for your help. Selene