Sirius Black gave Harry Potter a magical penknife for Christmas in 1994. It had attachments designed to open any lock and untie any knot, even if they have been protected against Alohomora or similar spells. To use the device to open a locked door, one inserted its blade into the crack between door and doorframe, then slide it up and down. However, there are some doors that cannot be opened by this knife, such as the door to the Love Chamber in the Department of Mysteries. That particular lock caused the blade to melt.