This would be a good application for webCoRE, which allows much more advanced logic than standard apps.
This will probably require 2 webCoRE Pistons (logical scripts).
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A simulated door sensor that follows the real door sensor’s state with a 30 second delay.
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Physical door sensor triggers playback of a 30 second long beeping track if the SHM is armed.
There are community forums to help you get started with webCoRE:
https://community.smartthings.com/t/introducing-the-new-webcore-community-forum/96259?u=etbrown