The latchbolt can be operated from either side of the door.  The lever set is secured from the inside of the door by depressing a pushbutton or other locking device such as a turn.  The lever set can be unlocked by engaging the inside lever, closing the door, or by an emergency release on the outside.
Growing up, my brother probably tried to get rid of all of the paperclips we had in the house.  Ignoring his threats of life and limb, I would maneuver the end of a paperclip into the outside of the doorknob and barge into his room.
                             
                            
                            
                                
                                    
                                    
                                        R-150 Stainless steel
                                    
                                
                                
                                    
                                    
                                        800 gms
                                    
                                
                                
                                    
                                    
                                        210 X 81 X 80 mm