I have what is known as privacy mortise lock with thumbturn, this (the inside):

enter image description here

PS: the hole in the picture is the door knob

  • Facing outside: a keyed mortise cylinder at the top, and a door knob at the bottom.

  • Facing inside: a thumbturn that is located a little lower than the (exterior) keyed mortise cylinder, and a door knob at the bottom at the same level of the exterior door kob.

I need to install a smart lock, and I have research many:

  • Sesame (installs over existing lock mechanism)
  • Sherlock (installs over existing mechanism)
  • Danalock (installs over existing mechanism)
  • Nuki (installs over existing mechanism)
  • August (requires installation over a rim lock it seems)
  • Friday (requires installation over a rim lock it seems)

Main problems are: there is no standard deadbolt inside, only a thumbturn, and the thumbturn is close to the door knob, not leaving too much space to install a smart lock hardware.

Changing the whole lock mechanism is currently not possible. This is a metal door, and the holes, specially the exterior ones, follow the building standard and can't be modified. Plus I believe the new lock systems are not that big, I'm not sure. Installing a whole new lock mechanism would probably require a new door.


  • Would it be possible to have the same keyed cylinder inside? What kind of lock/name is that where both sides are keyed? Will be compatible with the mortise mechanism in place? That would give me a keyed deadbolt inside, that most likely would allow me to install at least one that goes over the existing mechanism.
  • If the above doesn't exist or is not possible, then I'd have to deal with the thumbturn. In this case the Nuki lock seems to be most compatible one due to it's size. The Sesame is also interesting but it's too big and won't fit in the space.
  • Another option would be to insert a spindle where the thumbturn is, and then install August or Friday over the spindle.

Any experience or tips you can share?

Thank you!

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