Extra lock /global/scaled/524x224x0x0x524x-1/Other-ASSAOEM-Lock guide by ASSA OEM-Extralås 524x224.jpg To mount an extra lock is usually a simple way to increase burglary resistance on your door. And among those the hook bolt is usually preferable over a straight bolt. Extra locks are available in models for cylinder or lever.An extra lock provides greater security because of an extra blocking point in form of a bolt. Extra locks comes with both a straight and hooked bolt. A hooked bolt is preferred, mostly because it connects the lock, and therefore the door with the frame. A lot of people also install an extra lock to get one extra unique key. This can be useful if you sometimes need to leave out a key for others who needs temporary access. However, it is not certain that your door is prepared for an extra lock, and this will require a professional to make sure the installation is done correctly. You should contact your door supplier so they take a look at the door before you do anything. And that should be done so the warranty isn't affected.