I was honored to have a Hackaday front-page article of iDONT! Much better description of the project than I could ever come up with...

I have been playing with a Non-Invasive Current Sensor that works with AC currents. Along with the ESP's built-in ADC and a conditioner circuit described here, doorbell presses when the doorbell is on/active can be detected. This would be good for logging and maybe additional smart home features which are beyond the scope of this project.