[repost] Fail Safe vs Fail Secure

I didn’t write this article. I don’t recall when and where I copied it for my learning reference. If you are the author and don’t approve of my reposting it, please kindly let me know (flecherfeng@gmail.com).

我平时做security audit时,经常会碰到这个问题。




正如文中指出的,Fail safe 关注的是people are safe. Fail secure关注的是place is secure.

Fail safe和fail secure不仅是锁闭装置的两种设置理念,也体现了HSE和Security两个专业对紧急事件的不同理念。

Voluntarily or not you’ll eventually stumble across the fail safe vs fail secure questions. Should the lock be fail safe or fail secure?

Fail safe vs Fail secure Definition

   Fail safe: The lock unlocks when power is removed

   Fail secure: The lock unlocks when power is applied

Fail Safe Locks

When looking at fail safe locks this means that it’s default state is actually unlocked. To keep it locked during normal business operations, power is applied. Should the power be interrupted or fail, the door automatically unlocks or releases to let people out of the space. That’s why it’s called “safe” – it’s safe for people – not the space!

Mostly fail safe locks are used for main entry points like office doors or lobby access doors. A popular use for this application are maglocks which – by design – require power to operate.

Fail Secure Locks

So in the end fail secure means that if the power is interrupted or fails, the door stays locked. That’s why it’s called “secure”: It’s default state is locked or secured. So a fail secure lock locks the door when power is removed.

Often fail secure locks are used for IT rooms or other sensitive areas. However because the door keeps being locked in emergencies, typically it will be usable with a mechanical override, such as a regular key. However this is also a way of getting in the door without leaving any electronic traces. This is why the use of mechanical override keys is often restricted to only a few people who are highly restricted in use, naturally that would be to complex for too many members to operate.

Fail secure locks are used for fire related doors or staircase (stairwell) doors. The reason is that in case of fire, those doors should remain closed to seal off a portion of the space and help reduce spreading of the fire.

*Read more about the different types of electronic locks

1) Most common misconception

Most people would think that fail safe locks are there to allow fast exit in case of emergency. This is called “egress” and egress has always to be granted nevermind the lock. That means with a fail secure or fail safe lock you can ALWAYS exit the door or building – emergency or not. The terminology of fail safe or fail secure is only around ENTRY control which means it determines what happens in case of an emergency with entry. If all doors would be un-accessible during a fire – fire fighters or medical staff could be hindered to help properly.

2) Second most common misconception

Typically because people want to avoid fail safe locks from unlocking during power outages, they install backup batteries. However that is actually defeating the purpose of why fail safe locks have been installed in the first place.

One big reason why many offices do this is because glass doors which look a lot better are much more popular. Since typically only magnetic locks work on glass doors, the company wants to operate them like a fail secure magnetic lock – choosing the maglock only for the reason of it working with the glass door.

3) Third most common misconception

The third most common misconception is that electric strikes are only fail secure. In fact they can be configured for either ‘fail safe’ or ‘fail secure’. What makes electric strikes work are actually solenoids (magnets) inside of the strike shooting back and forth a little element to lock and unlock the strike. So depending on the polarity of the solenoid it can be movable when loosing power or stay in position.


Fail secure locks are definitely the standard electronic lock type, but if you are more deeper thinking about security you should consider enter scenarios and that’s exactly when fail safe locks come into play. A smart move is to get an electric strike that can be configured for both fail secure and fail safe. So if you ever want to switch the operating mode, you flip a switch instead of replacing the lock.


  1. 所有紧急逃生门按照HSE规范设置,规定颜色、碎玻或推杆门、门外侧不能有把手、门内外通道不得阻塞、设置醒目指示标识、逃生门不得用于日常人员通行、设置本地加远程报警联通security control center
  2. 机房、剧毒品库等重要部位应配置专用锁闭装置,火灾时保持锁死,并触发报警联通security control center。安全监控中心的保安应能立即实时得到该部位的监控画面,以决定如何处置意外情况(例如该部位恰好有人作业)。为防止这个场景下的极端意外情况,如该部位锁死后,作业人员被困其中,监控失灵,监控中心无法获取该部位实时画面,应考虑在这些特殊部位安装应急报警器,确保能向监控中心求救。