In September 2021, the Nest Cam Battery does not have a built-in speaker or the capability to play alarms directly. Therefore, it is not possible to have an alarm played on the camera itself.
Regarding your Nest Hub Max, while it has a built-in speaker, the option to play an alarm when a person is detected by the Nest Cam Battery is not available through the Google Home app. At present, the Nest Cam Battery and Nest Hub Max do not have direct integration for triggering alarms based on camera activity.
As for the Nest Protect 2, it is primarily a smoke and carbon monoxide detector and does not have the ability to integrate with the Nest Cam Battery for triggering alarms based on camera activity.
However, I recommend checking for any updates to the Google Home app or firmware for your Nest devices, as new features and capabilities may have been introduced since my knowledge cutoff. Additionally, it's worth reaching out to Google Nest support or consulting their official documentation for the most up-to-date information and to inquire about any potential workarounds or future feature releases that may address your specific needs.
