The Google Nest Doorbell (wired, 2nd gen) is made to work with your home and stay powered by connecting to the doorbell system wires. But many homes will need to upgrade the doorbell system’s transformer to be compatible with Nest doorbell.
Nest Doorbell (wired, 2nd gen) has a voltage requirement of 16 to 24 VAC and a power requirement of 10 to 40 VA. You can usually find the system transformer’s voltage information inside the doorbell’s chime box, as well as in or near the breaker or fuse box.
If the system doesn’t meet the power and voltage requirements, or if you’re not sure, contact a local certified electrician to service your doorbell system before you install your Nest doorbell.