Almost all car alarm sensors have settings arrangements inside them. It’s a good idea to get the owners manual of the car alarm that you have and read up on it. The manual will have instructions on how to locate the shock sensor and turn down the sensitivity. The sensor arrangement is different on most cars, and you will have to wait for 60 seconds after resetting the system. This will allow the alarm time to fully arm itself. This option may not be present on the newest electronic alarms where these levels are electronically preset.
For more info, see Car Alarm Programming Basics