Mul-T-Lock MT5+: Three Locks Hiding Inside One Cylinder.

Mul-T-Lock's signature technology, and the oldest of the three. Each pin stack is a pin within a pin — an outer sleeve and an inner pin that move independently, each of which must reach its own shear line. Documented

Compare that with an ordinary five-pin cylinder, where five chambers means five things to set. Here five chambers means ten independent elements, each needing to land correctly and stay there while you work the next.

The key does two jobs at once: dimple-style cuts on the flat of the blade address the telescopic pins, at depths that drive the inner and outer components differently. Manufacturer Mul-T-Lock describe the MT5 platform as using five telescopic pins, with some cylinder variants running ten telescopic elements.

This alone puts it far beyond anything on the budget end of the market. But telescopic pins are decades old, well understood, and dimple-lock pickers have been working on them for a long time — which matters in Chapter 4.

The locking bar is what the plus sign refers to, and it's a sidebar by another name. Documented

• A set of finger pins sits at ninety degrees to the key pins, with tiny fingers protruding into the edge of the keyway.
• A milled pattern along the side of the key — entirely separate from the dimple cuts — pushes those fingers to their correct positions.
• Only when every finger pin is right can the locking bar retract, regardless of what the telescopic pins are doing.

The detail that matters to anyone trying to open one: the finger pins are full of false gates. Community That's the same idea as a spool driver in an ordinary lock — deliberately feeding the attacker feedback that feels like progress and isn't — applied to a sidebar.

The milled pattern also does commercial work. Because it can be varied independently of the bitting, Mul-T-Lock use it to create exclusive keyways for individual dealers — a geographic monopoly on blanks enforced by the shape of the key.

The cleverest of the three, and the one with a date attached.

At the very tip of the MT5+ key is the Alpha Spring — a mobile, sprung element built into the key itself rather than the lock. When the key is fully inserted it engages a dedicated pin at the rear of the cylinder, creating an additional shear line that doesn't otherwise exist. Documented

Think about what that does to an attacker. The final security element isn't a component you can study by looking into the keyway — it is only created when a genuine key is present. A picker working from the front of the cylinder is trying to satisfy a shear line that a correct key brings into being.

Three mechanisms sounds unbeatable and the engineering genuinely is impressive. The record is more nuanced, and a buyer spending $200–$330 deserves it.

The thumbturn problem is the one to act on

Of everything above, this is the finding with a practical consequence. On a single-cylinder deadbolt — key outside, thumbturn inside — a bypass that reaches the thumbturn makes the cylinder irrelevant. It doesn't matter how many mechanisms are in it if the attack never goes near it.

This isn't unique to Mul-T-Lock. It's a category-wide issue and it's the same argument we make about letterboxes, pet doors and glazing near a thumbturn: any path to the inside handle defeats the entire lock. What's notable is that it applies to a flagship high-security product, and that no amount of cylinder engineering addresses it.

Both are flagship high-security cylinders and they solve the problem in opposite ways. The MT5+ takes the pin tumbler and stacks conditions onto it until it becomes intractable. The Abloy Protec2 abandons pins entirely for rotating discs and a sidebar.

The previous version of this page called these "different roads, same destination." Having read both records properly, we'd revise that. The destinations aren't identical. The Abloy resisted the public locksport community longer, has fewer practitioners capable of opening it, and doesn't have a published curriculum.

Where the MT5+ answers back is the ecosystem. The magnetic card and dedicated cutting machine give a facilities manager a paper trail and a hard stop on duplication that works regardless of anyone's picking ability — and for most buyers of a lock at this price, unauthorised keys are a far more realistic threat than a specialist at the door.

Buy it if

• Key control is your actual problem. Staff, tenants, contractors, shared buildings. The card-and-machine system is genuinely strong and doesn't depend on patents.
• You need serious master keying. The platform supports large, complex hierarchies — a real advantage over most high-security options.
• You want UL 437 in a residential deadbolt form factor with a fire-rated bolt and ANSI Grade 1.
• But ask about MTL800 first. It is Mul-T-Lock's current platform, uses a double alpha spring under newer protection, and is fully backward compatible with MT5+ tooling and cutting machines.
• Double cylinder is an option for you and local code permits it — that removes the thumbturn bypass from the picture.

Buy something else if

• Manipulation resistance is your single priority. The Abloy Protec2 has the stronger record.
• You haven't reinforced the frame. Non-negotiable. A $300 cylinder on a jamb held by 3/4-inch screws is the most expensive way to change nothing — four dollars of screws matters more than this entire purchase.
• There's glass, a letterbox or a pet door near the thumbturn. Fix that first; see the perimeter walkthrough. Any reach-through defeats the best cylinder made.
• You want a lock a locksmith can service anywhere. Restricted systems mean going back to the dealer.

The MT5+ is what happens when a company refuses to abandon the pin tumbler and instead keeps adding conditions until the thing becomes genuinely hard. Telescopic pins, then a sidebar full of false gates, then a spring in the key that conjures a shear line into existence. It is inventive in a way very little hardware is.

It is also, precisely because it is a flagship, one of the most studied cylinders in the hobby — picked on video for a decade, picked blind, and taught. And on a thumbturn deadbolt, none of it engages, because the attack goes around rather than through.

That's not a reason to avoid it. It's a reason to buy it for what it's genuinely best at, which is knowing exactly who holds a key — and to spend the next four dollars on the frame.