The act of an agent communicating (service provider, social media, etc) their arrival by registering/confirming for a previously reserved service (e.g. flight check in) or at a place (e.g. hotel), possibly resulting in a result (boarding pass, etc).<p>Related actions:</p><ul><li><a href="http://schema.org/CheckOutAction">CheckOutAction</a>: The antagonym of CheckInAction.</li><li><a href="http://schema.org/ArriveAction">ArriveAction</a>: Unlike ArriveAction, CheckInAction implies that the agent is informing/confirming the start of a previously reserved service.</li><li><a href="http://schema.org/ConfirmAction">ConfirmAction</a>: Unlike ConfirmAction, CheckInAction implies that the agent is informing/confirming the *start* of a previously reserved service rather than its validity/existence</li></ul>.