I stumbled on this post as I was about to post my experiments today. I had a spare SmartThings Open/Closed sensor that I tried to trigger with the magnetic coil of the bell. It seems that the SmartThings reed switch is not as sensitive as the switch that Johnny_Davy used, or my doorbell does not have as strong a magnetic field. Our doorbell looks very similar to wackware’s.
I had to remove the sensor from its housing and shove it in the small space right next to the coil to get the open/close trigger. I wanted to turn on a light when it closes, but then had to write my own SmartApp, as the existing apps all seemed to work on sensors being NC and not NO, which how the sensor behaves in the coil field. I.e. open is the inactive state, and it closes when the doorbell gets triggered. So I now have a simple SmartApp that will turn on a ligth for 30 seconds when the doorbell rings.
I am probably going to desolder the reed switch from the circuit board of the sensor and attach a wire to it. That will allow me to put the sensor back in its housing and mount the reed switch right next to the coil. That will simplify future battery changes. At the moment everything is held together with scotch tape and blue tack. And I don’t mean that figuratively:).