Check in/Check into

(A) To report to someone when you arrive at a place or be given a room. (inseparable)

1. Passengers must CHECK IN one hour before the flight.

2. We CHECKED INTO a hotel. 

3. She was about to CHECK INTO the hospital.

4. When I arrived in New York, I CHECKED INTO the hotel and went straight to bed.

5. The receptionist said guests cannot CHECK IN before 4 pm.