to find out what someone is doing in order to make certain that the person is behaving correctly or legally:
Checked in into them
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to say who you are when you arrive at a hotel so that you can be given a key for your room:
Checked in into them meaning & definition 1 of Checked in into them.
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to go to a desk at an airport, port, etc., or a hotel and say that you have arrived:
Checked in into them meaning & definition 2 of Checked in into them.
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