Airport check-in 
The check-in process at airports enables passengers to check in luggage onto a plane and to obtain a boarding pass. Each airline provides facilities for passengers to check in their luggage, except their carry-on bags. This may be by way of airline-employed staff at check-in counters at airports or through an agency arrangement or by way of a self-service kiosk. The luggage is weighed and tagged, and then placed on a conveyor that usually feeds the luggage into the main baggage handling system. The luggage goes into the aircraft's cargo hold. The check-in staff then issues each passenger with a boarding pass.
There is an increasing trend towards more streamlined checking-in processes, whereby passengers can bypass or reduce the time in queues at the staffed check-in counters. This may involve passengers checking in online before arriving at the airport or using an airline's self-service check-in kiosks at the airport. Some airports have curbside check-in, where passengers can check in their bags to an airline representative before entering the terminal and then proceeding directly to security.
At a hotel or similar establishment, guests are usually required to check in, which involves providing or confirming the guests' personal information and providing a signature. The establishment may require guests to provide a credit card guarantee to cover potential costs such as room service for the duration of the stay. At the end of the check-in, the reception staff will provide guests with a room key.
The hotel's check-in time indicates the time from which the hotel starts charging for the day. If a guest wants to occupy the hotel room before the hotel's check-in time, the hotel charges for one additional day and considers it as a previous day's stay (as compared to occupying the hotel room after the check-in time). Most hotels, however, can accommodate a little buffer time request (typically 30–60 minutes) by the customers, without any additional charge, if one wishes to take the room before the check-in time. For the most cost-effective usage of hotel room occupancy, the customer should try to reach at about hotel's check-in time and leave or hand over the hotel room at about the hotel's check-out time, but it may not be always practical because the customer's arrival and departure time of flights may not align with the hotel check-in and check-out time and for other reasons.
Social network 
Many social networking services, such as Foursquare, Google Latitude, Google+, Facebook, VK (social network), Gowalla, GetGlue and Brightkite, allow users to "check in" to a physical place and share their locations with their friends.
Many applications have a “Places” button or tab where a user can see a list of nearby places into which the user can check in. If a location is not on the nearby places list, the user can add the location directly from the phone. Once users have checked in, they have the option of sharing their location with friends in services such as Twitter or Facebook.
Since the check-in became a ubiquitous mechanism in most mobile applications, the industry especially in the gaming branch has tried to find alternatives. Gaming applications in particular require the user to check in multiple times in a row, so the mechanism becomes a sustained routine. Currently, possibilities for an auto-check-in are tested by developers.
- Riva Richmond (September 10, 2010). "Three Best Ways to Use Location-Based Social Media". The Wall Street Journal. Dow Jones & Company, Inc. Retrieved September 30, 2010.
- Christian Paulus (August 08, 2012). "Getting rid of the check-in mechanism". geosocialgames.com. Retrieved September 25, 2012.