Continuous beep on opening driver door
 

I have a 96 honda civic dx. Days ago, I forgot to close my door and the cd player was stolen. After that, every time I open my driver door, a continuous beep will be on even if the engine is off. This never happened before that.
I installed a new cd player later and it can be turned on even if I havent plugged in my key. Now my battery will be dead if I havent driven my car for two days.
Anyone knows how I can fix the problem?:(

That's the key reminder beep. The thief probably tried to bust the ignition lock and in the process, broke the switching mechanism. Even when you turn it "off", it's not really off, so the CD still plays and the battery runs down. Also the car thinks that you have left the key in and is beeping to remind you.