Hello holocron and those that may be looking at this thread.
I agree, smaller mounting holes result in less structural loss and easier installation. The external reed switch approach has these additional advantages:
The sending unit’s operational LED can be observed directly.
Battery changes are through direct access-no partial disassembly with tools are required.
Below are some links that delve into the details:
My Wyze Smart-ish Lock Another Approach This link gives the general approach for an external reed switch installation.
Contact Sensor Modified - Magnetic Reed Switch Remote / Outside This link goes into details of the actual reed switch modification.
Hiding the Contact Sensor No Chiseling No Sawing This link shows how a contact sensor sending unit can be recessed into a door or its frame by drilling a sequence of small holes.
As I write this post another thought occurs to me of using an auxiliary device that uses an unmodified contact sending unit. The auxiliary device would consist of two small wire coils connected to each other via a pair of wire leads. One coil of the device would be placed in a small hole in the wall near the end of magnetic bolt and the other coil will be on the wall’s exterior surface in contact with the sending unit.
Movement of the dead bolt would induce a current in the nearby coil, which would create a magnetic field in the other coil that triggers the reed switch.
Experiment time.
Victor Maletic.