Security System Killing Battery

Hey guys, I could use some help. I have a 2001 eclpise GT.

Ever since I bought the car the security system would randomly go off. It has gotten to the point where it kills my battery. I have had to resort to taking off the battery cables everytime I park the car or else I will not be able to start it. I have changed the battery too and it hasnt solved the problem. I would like to know how to Disable to the security system so that the lights and everything wont kill my battery. I have tried already to disable it but couldnt, so I just turned off the horn so it would not annoy people.

Thank you for any help

Is it the factory one??

the factory one is only supposed to go off when a door/Hatch is opened.

which means you probably got water on some of your electrical somehow...the same things goes on with my Sequoia because my mom left the sunroof open when it rained, so now when it gets cold out the alarm always goes off....real lame...not sure what to tell you to do.