Car Alarm

Picture provide by www.nottinghamcity.gov.uk/.../b/car-alarm_1.jpg

Once every couple of weeks, I will walk out to my car after work, press the unlock button on my car, open the door, only to have the CRAP scared out of me from my car alarm blaring! Excuse me? Am I on candid camera? Why does this happen to me so often? Obviously, I pushed the unlock button, and my car is unlocked, so why is my alarm going off? And it doesn't happen all the time! It's like my car knows when I am most unsuspecting and then BAM! BEEP BEEP BEEP BEEP! Sooo embarassing! One time, I even scared a fellow co-worker who parked right next to me, getting into his car! I just said..'Sorry' as my whole face blushed and I rushed to get in the car and out of the parking lot! Heaven forbid my good friend C.D. be with me if this ever happened! She is so darn jumpy, she might pass out from it! Seriously, she is one of those people that if a car was coming her direction and it startled her....she would just stand there paralyzed with fear. You know those people you see on tv, Freddy Kreuger coming at you and they just trip and can't get up so they start crawling away crying...yeah..that's her! Sorry, went off on a tangent there...So my question is, What's the deal? What causes this?