Our house has a 90’s NuTone Intercom-AM FM and integrated doorbell. There is no separate Chime- the doorbell tone would come through all the interior speakers. I replaced the doorbell button with the Wyze unit- but the red/white wire from the NuTone provided 8.5VDC, and I could trace it to 2 terminals in the NuTone Unit. Within the enclosure box between the studs in the wall was an access door that contained the 24V AC transformer to power the Nutone unit. I was able to move the wires for the doorbell button to these terminals on the transformer and the Wyze unit powered right up, No sweeter words to hear than Ready to Connect when I went to the outside to check it out. I hope this is helpful to anyone else that has one of the Old School Nutone units