A double-sided deadbolt is a lock that in order to open or lock it you will need to use a key from the inside and the outside. Unlike most dead bolts and door knobs that have a button or flip in the inside part of the lock, double-sided deadbolts are operated with a key from both sides. IMPORTANT NOTICE: In certain counties the local fire department forbids us to install double sided dead bolts on residential doors. One of the reasons for that is in case of emergency (e.g. fire) the tenant has to leave the apartment quickly and may not have access to their keys, which are necessary to open this type of lock.