Detector locks defeat non-desctructive entry

It’s no secret that there are locks that are impossible to pick with traditional tools, but the number of locks that can’t be bypassed with specialized tools shrinks each year as engineers come up with new exploits. However, detector locks defeat non-destructive entry with a simple yet effective method. The locks simply indicate that they have been tampered with or unlocked.

What is a lock’s role?


When watching a lock exploit presentation by Deviant Ollam, Schuyler Towne, or Barry Wels, most of their discussions will be about defeating locks. They’ll shock you how the average lock in your home, that was purchased at a hardware store, is easily unlocked with a two dollar lock pick and tension tool in under a minute. There are more expensive “security” locks that are pick resistant or pick proof, but most of us only have access to these locks by purchasing them from specialized vendors online. However, many of these more expensive locks can also be bypassed by very elegant or rather ugly specialized attacks.

What’s usually only barely covered in lock discussions, is the more fundamental concept on where a lock fits into the physical access picture. Unless your lock controls the very heavy bolt of a strong room or safe, the lock does not prevent access, as it’s not necessarily the weakest link and can easily be bypassed. Doors can be kicked in or rammed, windows can be broken, and holes can be knocked through walls as part of a destructive entry. As a result, the easily picked lock is simply for pedestrian flow, to prevent accidental entry. A more secure lock, that can’t easily be opened without the proper key, can also act as an auditing tool that indicates that a non-destructive entry has likely not occurred if there is no evident damage done to bypass the lock.

Dangers of non-destructive entry

What is often considered the most important role of physical security is the prevention of access to what is in the container, what ever the container may be, such as a building or room. However, depending on the purpose of the container, the detection of an unauthorized access could be as important as the prevention of access.

Key pin with signs of picking

One of the simplest examples showing the dangers of non-destructive entry is the long term storage of large amounts of patient medical records, customer financial records, or some other personally identifiable information. The room storing these documents is hopefully locked, and the room is regularly checked for any signs of unauthorized entry. To a security guard, this will translate to “signs of forced entry”. Most organizations aren’t going to be regularly examining the lock protecting their long term document storage for the destructive signs of picking. As long as key control hasn’t been compromised, and the door remains locked, the organization will assume that the documents have not been tampered with.

However, with a set of lock picks, someone may have bypassed the key control and copied some or all of the documents. Additionally, due to the large number of documents being stored, no inventorying of the records is going to occur due to the expense and time involved, and up to 30% or more of the records may simply go missing without any obvious visual signs.

As with any data breach, one must first be aware of the breach to begin any investigation and mitigation of damage. As the time that a breach goes unnoticed increases, the ability to mitigate any damage drops significantly. The likelihood that an investigation results in finding the culprit or in the complete recovery of any of the data quickly fades. The recent breach of e-mail addresses and passwords of over 700,000 Gawker Media users went unnoticed for over a month, but it’s likely that many similar breaches have yet to be discovered.

Although non-destructive entry is often used to plant listening devices, hidden cameras, and to steal information, imagine a container full of gold bars, diamonds, or Stinger missiles where just a few go missing, unnoticed until an inventory occurs. Once the theft is discovered, imagine the difficulties determining when the items went missing and trying to piece together the now cold evidence. Now imagine coming home and finding that all of your windows and doors are still locked, their is no sign of forced entry, yet an intruder is in your home, waiting for you and your family to arrive.

Chris Jenks, long time lock picking enthusiast and founder of the A2 Lockpicking group, is quick to point out that an improvement in the locks that the local hardware stores carry is going to be one of the biggest influences on improved security and says “For the most part I don’t think the home users are going to care enough”.

Preventing non-destructive entry

Preventing non-destructive access begins with good key control, and using appropriate locks. One can purchase easily pickable Schlage and Kwikset locks at the hardware store. However, from specialty shops and online, one can also find pick resistant locks like the Medeco, and locks like the Abloy Protec which don’t have any published physical bypasses (at this time).

The trick is to use a sufficiently strong lock to delay entry long enough to deter the attacker or to detect the attempted bypass by video surveillance or sentry. Or alternately, force the attacker to do a destructive entry which can be easily detected.

Auditing non-destructive entry

Wilkes Detector Lock (Copyright V&A Images)

At the last A2 Lockpicking meetup in Ann Arbor, one of the attendees shared a video of a detector lock allegedly crafted by Johannes Wilkes in 1680. The video had no sound, and was very small, but together with the transcript, the video demonstrated a lock that had a counter on it to indicate how many times the lock had been opened. The Wilkes lock is part of the “Metalwork Collection” that resides at the Victoria and Albert Museum in London.

The most famous detector lock was created over a century later by Jeremiah Chubb and patented in 1818. The Chubb Detector Lock didn’t have a counter, but in theory, when tampered with, it would require a reset with the proper key before it could be opened. As a result, the lock would only “detect” an attempted opening of the lock, but would fail to indicate if the lock was opened without the proper key. The Chubb Detector Lock was successfully bypassed in 1851, by American locksmith Alfred Charles Hobbes, who successfully picked the lock, bypassing the tamper detection.

When auditing a non-destructive entry opposed to a failed attempted at a non-destructive entry, the Wilkes lock’s counting feature appears to surpass that of the Chubbs lock. By simply keeping track of the counter, one could tell if the Wilkes lock had been opened since the last time it had been opened by a proper key holder. However, the Wilkes lock had weaknesses in that the counter could be reset to zero upon being picked, and only counted up to 100. This would allow a successful picker of the lock to increment the counter to the original state if he or she could locate the counter reset mechanism and had the time to pick the lock multiple times.

Although both locks had weaknesses, both tamper detection and counting the number of times a lock has been opened appear to be great features that seem to be missing in most modern locks.

It could of course be argued that failing to bypass the auditing of a non-destructive entry is the same thing as a destructive entry.


Although a lot of time is being spent by lock manufacturers on the prevention of bypassing the locking mechanism, it seems that it would take little effort to also add a counter to a lock that was difficult or nearly impossible to bypass, to indicate when the lock failed to prevent access.

I’d like to see more modern locks indicate tampering and include tamper proof counters that indicate when an access has occurred. It would also be an interesting blast from the past.

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