Here you can learn about the three different types and their best uses.
BS3621 Sash-Locks
This is the most common type of door lock. As you can see from the photo, these offer a handle-operated latch, and a key-operated deadbolt to lock the door.
Sashlocks are popular with homes and offices as they allow you to close the door without locking it when you wish to keep the door closed but not locked, but it is not convenient if you dont want to physically deadlock the door via the use of a key. Of course you should always keep your doors securely locked when not in use to maintain security.
Summary - having a BS3621 sashlock on your door gives you a high security locking solution, with the option of having it held closed purely on the latch when you do not wish to repeatedly lock and unlock the door when entering and exiting.
BS3621 Dead-Locks
Deadlocks are particularly useful on doors that either have an existing latch on the door, or on doors where you do not want to allow latching and want to enforce proper locking of the door. These are often used in conjunction with rim nightlatches for example - commonly referred to as a "Yale Lock".
If you have an old rim nightlatch on your door that suits the aesthetics of the door and your insurance company is demanding you have BS3621 locks fitted, you don't need to change your traditional style nightlatch! You can continue using it, but simply fit a deadlock further down the door at waist height, to allow for a good strong level of security to be applied when the deadlock is being used. This will satisfy the requirements of BS3621, and you would not need to replace your old style nightlatch - which we all know often suit older doors a lot better than the modern types!
Summary - having a BS3621 deadlock on your door, allows you to have no latch on the door, or to continue using your lovely old Yale type latch, as long as you use the new deadlock to fully lock your door!
BS3621 Rim Locks
Rim locks are surface-mounted locks that are not morticed into the door. They are fitted on the inside of the door, and engage with an external keyway which allows for unlocking via key from the outside. Please note that you must use key to unlock the door from the outside, unless the bolt has been disabled via a "latch snib" from the inside for some types of this locks.
Those locks are probably the most popular in the UK, and are commonly referred to as "Yale Locks", due to the fact that the pin tumblr type cylinder used on these was designed by Linus Yale. Yale are not the only manufuctorers who make these locks, and therefore giving you more choice of brands style, security and sizes.
Those locks have the advantage of allowing you to simply close the door and not have to worry about locking it yourself. This is no doubt why they are such a popular choice, as they allow for fast and convenient use and only requiring you to unlock via key when entering the property. And with the majority of rim nightlatches, you also have the ever-loved 'latch snib' which provides a hold-back function for the latch to allow the door to stay unlatched and therefore unlocked. The downside of this lock, is you may find yourself locked out more often than other locks, as often we leave the house without the keys and by the time you realise it, its too late as the door is shut behind you.
Summary, having a BS3621 Rim Nightlatch Lock on your door, gives you the freedom to not have to physically lock your door every time.
Note: Be aware that officially there is no such thing as a categorically "insurance approved" lock. This is a common term widely used for the BS3621 kitemark, as the majority of insurance companies require this standard if any. However different policies for different properties which may have different requirements, it is therefore advised to double-check your policy and give your insurers a call if you are not sure!
