Most convertabile alarms are like that. The dont tend to go off unless someone is leaning against the door or hits something inside the car. Its easy to steal anything inside an open topped convertable, not just from BMW's. So its better if u leave the car unnatended dont leave anything valuable in site, lock em in the glove box or better yet leave the top up. It may be more work but its better than having someone steal your $300 iPod.