How do I disable my car alarm?

I have a honda civic esi which I bought last year for a run around. It had I was told a piranha car alarm fitted but this was disconnected. I have had to charge the battery up on it putting it back into the car the as soon as I turn the key or touch a pedal (its an automatic) the alarm goes of and I am unable to star it or come to that do anything else. The question is does the honda come with an immobiliser factory fitted or is the Piranha still fitted Either way how do I swith it off 'cus I can't use the car!!
I am asuming that it is factoryfitted as I have not had any 'alarm' issues till now
Grateful for any advice.