On a typical door – either wood, metal, or plastic (yes, that’s not a typo, a lot of new doors are made of a plastic shell filled with foam) – there are two locks: a doorknob lock and a deadbolt.
Deadbolts come in two types – single-sided (or “single cylinder”) and double-sided (“double cylinder”). A single-sided deadbolt uses a key on the external side of the door, and has a thumb-turn (no need for a key) on the internal side. Most fire codes recommend or require single-sided deadbolts in order to ensure easy escape in case of a fire; anyone stuck in a burning building will not need a key to get out. But private homeowners can decide what type of lock they prefer to have on their door.
The disadvantage of a single-sided deadbolt is that if there is any type of window next to or within the door, it is relatively simple for an intruder to break the glass, reach in, and unlock the door using the thumb-turn.
A double-sided deadbolt includes a key-way on both sides of the door – the lock can only be locked or unlocked from the inside and outside by using a key. The advantages and disadvantages of a double-sided deadbolt are the opposite of a single-sided one.
Our recommendation is to have two sets of deadbolts on external doors. Immediately above the doorknob we recommend installing a single-sided deadbolt for daily usage that can be locked when people are inside the house. Above that we recommend installing a double-sided deadbolt that can be locked when the house is empty or when you will be away for long periods of time – e.g. if you leave the house during the day for work, go on vacation, go out to visit friends or family, etc.
The two deadbolts should be enough to secure your home, so we recommend installing a simple passage doorknob on external doors that does not include a lock. This will make sure that you do not lock yourself out by accidentally closing the door behind you. But if you prefer to have an extra layer of security you can install an entry doorknob, which gives you the option of using a key to lock it from the outside.
There are hundreds of types of locks on the market, and thousands of ways to combine them. When you are choosing how to secure your home, be smart, and make sure to consult a professional locksmith to find the best solution to protect you and your family.