[zyberzero]

I did something similar, but as I didn’t have access to mains in an easy way (read: close enough to the doorbell) to power the ESP I built a small PSU that took the very unregulated 8VAC from the doorbell transformer into 5VDC (using a rectifier, LM7805 for regulation and some capacitors to smooth everything out). Everything was small enough so I could hide it in the actual doorbell as well!