All too often, students lock their room door by turning the small button the back of the lock and closing the door behind them, and then accidentally leave their keys inside the room.
A call to a locksmith so you can get back into your room can be costly.
However with most room door locks, you can lock the door with the key.
To check if your lock works this way simply close the unlocked door, insert the key in the knob and turn it in the opposite direction that you would normally turn and the door will lock.
If you get into a habit of locking the door with your key every time, it will ensure you that you will not lock the keys inside of your room.