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"The DA20 has an adjustable delay circuit which allows you to keep the door open for up to 21 minutes without it responding. After this delay, it emits a loud pulsing tone to alert you to the fact that the door has been left open. Once the door is closed, it resets to its monitoring state. Because of the delay feature, you are not forced to listen to an annoying sound while you want the door open. It will let you know when it has been left open however."
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