safe deposit lock guide

Safe Deposit Locks: The Complete Guide

This guide is designed to describe major aspects of safe deposit locks, from knowing the main differences and advantages of each type to helping you make the right decision when choosing ideal locks for your new safe deposit box project and aftermarket services for banks and commercial safe deposit locker providers.

What Is Safe Deposit Lock?

A safe deposit lock is a dual controlled lock that requires two different keys to unlock at the same time. As these locks are mostly used on bank safe deposit boxes, they are commonly referred to as safe deposit lock, safe deposit box lock or SDB lock.

typical safe deposit lock

A typical big nose and small nose right handed safe deposit lock

The whole idea is to have the lock secured by two separate locks inside one lock housing that together control the lock bolt for a much higher security purpose. Not only two different locks can create a much higher code combination, but the renter identification process by bank employees may also add extra security.

Furthermore, the main security concept of safe deposit locks is the dual identification process, so it doesn’t have to be a mechanical lock with two key locks inside. In the modern banking industry, the electronic locking system is favored by its ease of use, multi-functional features and high-security performance. Many lock manufacturers have come up with electronic safe deposit lock products to serve the growing needs. While electronic locks are more popular and automatic, traditional dual key locks are still largely installed and serviced nowadays. We will talk about electronic safe deposit locks later.

How Does Safe Deposit Lock Work?

Traditionally, the safe deposit lock has two locks inside, with two keyholes on the lock surface. The key closer to the door hinge is called the “Guard Key” which is kept and maintained by bank employees or vault custodians. While the other key is called the “Renter Key” which is kept by renters. Obviously, as stated before, the lock needs to be opened by both correct guard key and renter key. The guard key is first inserted into the lock plug closer to the door hinge, successfully opens the guard lock and left in the open position. Then the renter key can be inserted into the renter lock plug to open the entire lock bolt. If either key fails, the lock won’t open.

People may get confused about which is the renter key and guard key. There is an easy way to understand the mechanism behind the lock so we can get it right once and for all.


The big lock plug is renter key, the small lock plug is guard key.

To open the lock, we need to retract the lock bolt. Imagine there are two locks, the renter lock and guard lock inside the lock housing, controlling the same lock bolt. The lock farther from the lock bolt is blocking the lock closer to the lock bolt from retracting the bolt. So we need to open and release the blockage from the farther lock first to be able to go to the next step. As the guard key is inserted first, so the lock farther from the lock bolt(at the same time it is closer to the door hinge), is the guard lock/guard key. The other one is the renter key for sure.

Types of Safe Deposit Locks

There are many variations of these safe deposit locks due to their mechanism, functions, features and sizes. We will talk about several main sectors that are important for us to consider when choosing locks.

Mechanical and Electronic

We will mainly talk about mechanical locks here as they are still the priority lock option for banks and commercial service suppliers yet being largely used and serviced.

There are also combination safe deposit locks to meet the diverse needs of customers who do not enjoy keys.

combination sdb lock

A combination safe deposit lock

Lever and Cylinder

Most safe deposit locks use lever tumblers as the core mechanism, the lever mechanism is highly favored by the banking industry. They are reliable, stable and rarely fail.

While some manufacturers would use cylinder lock or other mechanisms instead of lever tumblers, it’s not a big difference as long as they are good quality and high security.

sdb lock from abloy

A two mechanically operated cylinder lock from Abloy.

We will mainly talk about lever tumbler safe deposit locks in this guide.

Changeable and Fixed

A changeable safe deposit lock can be changed to accept new keys directly without the need to disassemble the lock case via change tools.

A fixed safe deposit lock, as the name suggests, is non-changeable and cannot accept new keys. To change the keys, you need to disassemble the lock to re-order the levers inside to match a new key, which is typically like assembling a new lock.

Some locks have one fixed and one changeable lock plug to serve customers’ purposes as well.

Why do we need changeable locks?

Let’s take a look at how a safe deposit box is rented and surrendered.

First, customers rent a box, get renter keys, deposit their properties. No doubt.

When customers don’t want to rent anymore, they give up the box, return all renter keys and withdraw all their properties. Everything seems fine.

What if the key is copied?

Things happened that customers claimed a large amount of cash and assets were stolen from the box. It turned out that it was the prior customer that opened the customer’s box with a copy of the renter key after the box was surrendered.

It happens and happens a lot.

box open

If you have the same key copy, you can open the same box.

When the renter returns with a single key claiming one key is lost, we are all aware of the importance of changing keys or changing the lock.

But in most cases, all renter keys are returned, do we still need to change?

Plus, it is not illegal to duplicate safe deposit keys, and the safe deposit locks are not only used on bank safe deposit boxes but also used on quite some safes and cabinets. It makes sense that you need to copy a key for your own interest.

It’s not mandatory but it is strongly recommended to have the lock or keys changed every time before the box can be rented again to ensure renters are receiving the only two keys that can open their new box.

For fixed locks, you can have bank staff to simply install new locks, switch locks between boxes, or to have a locksmith to disassemble the lock and reassemble it to new keys.

fixed safe deposit lock

Fixed safe deposit lock is very stable

With changeable locks, you can easily set the lock to new keys without any lock knowledge or skills and no locksmith necessary. It’s quite easy and pretty fast. And for banks to cut expenses, changeable locks are also favored in this case with less lock replacing costs and locksmith costs.

Are changeable locks the absolute winner?

Let’s look at another major factor – the mechanism inside.

When it comes to changeable locks, though the overall mechanism is all lever tumblers, the changeable part is different. There are two major designs: changeable levers and changeable fence.

Steve Young has an in-depht article on safe deposit lock servicing which shows how they look like.

Changeable lever design is mostly seen on early locks, such as LeFebure series. These locks are non-handed due to their changeable lever mechanism and double changeable.


Changeable fence design is still widely used to this day and is often seen on high security changeable key locks too. The changeable fence can be applied on either renter or guard lock or both locks, so we can have one fixed and one changeable lock and double changeable lock to perfectly serving our needs.


We don’t have to dig into how and why each mechanism works in detail, the whole concept of how to reset to new keys is mostly the same. In plain words, we use the old keys to open the lock first, then we use change tools to loosen the mechanism of the lock so the levers inside are released to be able to accept new keys. Then we switch to the new key, making sure the new key is well reset and then tighten the lock again.

It doesn’t require rocket-science knowledge to change a key, actually, it is quite fast and easy.

But many vault custodians/bank staff don’t understand the mechanics of how keys are actually changed, and they are not paying much attention when changing them. Sometimes the levers inside are not well-aligned when resetting and may slip after several times of successful opening and finally lock in.

For fixed locks, the levers cannot be changed or released, it makes sense that they are more stable compared to changeable locks, and they rarely fail.

To use fixed locks or changeable locks, it all depends on how your safe deposit service is going, how soon do you need to change locks, that’s it.

Left Hand, Right Hand, Non Hand

Left Hand (LH) locks are installed on a door hinged at the left.

Right Hand (RH) locks are installed on a door hinged at the right.

Non-handed locks are installed on either door by just flipping over.

Most of the safe deposit locks that we use are right-hand locks. The left-hand locks are generally used on the last row of boxes that are near the wall when the right-hand lock cannot fully open.

L.H. and R.H. locks both installed on the SDB

Number of Levers

Commonly safe deposit locks contain 5~7 levers, the more levers it has, the higher key combinations it can provide. While the renter lock usually contains 7 levers, the guard lock may have fewer levers for about 5~7.

Safe Deposit Box Key

Safe deposit lock keys are usually lever lock keys with small key bows. Sometimes when people happen to find a key hidden in their house, they want to identify if it is a safe deposit box key.

If it’s a safe deposit box key then it means one of your relatives may have a safe deposit box with estate in the bank that you might need to claim.

Here are some hints on safe deposit box key identification.

If you find a safe deposit key with an envelope that says “Keep one safe deposit box key in this envelope”, then it is a safe deposit key.

Additionally, when you rent a safe deposit box at the bank, you are given two renter keys by the bank in case you lose one of them, so if you found two same keys, then they are probably keys for a safe deposit lock, which means you may have a rented safe deposit box somewhere.

A safe deposit box key envelope to store the keys

If you only find a key with no other hints, then safe deposit box keys usually look like this. They might have different key bows or key lengths, but they all look alike.

Safe deposit box key images

Where to Keep Your Key

Keys are important, and you’d better keep them safe. You can choose to keep them at the same place together or keep the two keys in different places in case someone finds them.

You can hide it in your safes, favorite hidden places in your home, in your office, or somewhere completely “outside the box”.

Anyway, if you are not a frequent user of the safe deposit boxes, you’d better keep all your two keys in the same place. If you keep them separately, it’s highly possible you may not remember any hiding location in the end.

When you lose any of your keys, you might need to bring all necessary documents to the bank to drill your box and change the locks, which may cost extra money.

Safe Deposit Box Key Duplication

Usually, the keys are prohibited from duplication as it can significantly increase the risk for the box to be opened by thieves. There are news reporting thieves using duplicated keys to steal several hundreds of boxes at a bank.

So normally, there is a “Do Not Duplicate” sign on the keys so locksmiths won’t duplicate them. But many locksmiths do not care or are tricked by people who claim they happen to lose one of their keys and duplicate your key.

When you lose one of your keys, do not even think about duplicating another one. Go straight to the bank and ask for a lock change.

Keep your keys safe!


The safe deposit lock industry carries its major weight in the banking and safe storage business to this day. As self-service and automated safe storage system is trending, security suppliers need to invest more in the development of reliable and innovative safe deposit lock solutions to meet the ever-changing needs of the global safe storage market.

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