If your Sentry doorbell is completely unresponsive, i.e. no lights, no sound, and cannot be reset, regardless of whether it’s powered by USB or doorbell wires, please read ahead. Otherwise, you can try resetting the doorbell.
This issue is most likely to happen during or after a firmware update. If the Sentry video doorbell lost power or the voltage was not stable during the update, then the update will fail, resulting in a “bricked” state.
To resolve the issue, simply manually update Sentry’s firmware. Please use a 5V 2A micro USB adapter to power the Sentry doorbell during the manual firmware update to provide the most stable power.