If there is a biometric screening system for a locked door, can one do biometric screening on shabbat? In this case, this is a completed circuit with running electricity before Shabbos (it’s always running), but it does certain actions (such as unlocking), when it does biometric detecting. Would it be acceptable?

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    Interesting idea, but at the heart of it, as you suspected, the electronic unlocking makes this a duplicate of your "clap on-clap off" lamp question. Commented Oct 10, 2023 at 21:46
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    the clap activated circuit is always listening the same way the biometric circuit is always scanning, and you build a circuit to activate the door mechanism the same way you do to turn on the light. At least on a halachic level. Commented Oct 11, 2023 at 7:30
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    It is the same concept, absolutely. I am not aware of a single posek who is lenient on electronic keycards, however. Commented Oct 11, 2023 at 7:36

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Even if the "listening" circuit is always on, the "action" circuit is turned off until activated. When anything comes near the sensor, it immediately springs into action, searching its database for a match. If the object is a match with its verified fingerprint, it sends a message to the lock to open. That's a lot of circuits opening and closing. Hence, it would be as assur as turning on a light.

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