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 most likely happens during or after a firmware update. If Sentry somehow lost power or the voltage was not stable during the update, then the update would fail, resulting in a “bricked” state.
To resolve the issue, you would simply need to manually update Sentry’s firmware. We highly recommend using a 5V 2A micro USB adapter to power Sentry during the manual firmware update to provide the most stable power.