Ideas of questionable quality

[Kovirii]

It should react when dangerous stuff goes through, but only give a name if it went through the checkpoint at the same time (or almort, a delay could be added if no ID was instantly caught) as an ID, in which case it should report that ID (Or multiple IDs if you happen to wear a bunch of them for whatever reason).
That, or Frank_Stein's snapshot idea which is nice too, a small square one centered on the checkpoint, so that you can still go through it "safely" by throwing for farther away, making it more obvious if someone is around.

This.

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Give the Janitor closet a utility belt. Most of the janitor's tools fit on a belt and no I'm not biased.

Oh, and give the detective a security belt? Or a utility belt. Whatever.