Planet NVR-820 User Manual page 72

Define which system events should trigger the recorder to send out notifications.
Define how the notifications will be sent and where they will be sent.
Event trigger may not work for cameras that are placed outside of your local
network or on the Internet until the "UPnP Port Forwarding" is enabled in both the
NVR and the router.
Network Video Recorder with HDMI
72
NVR‐820 / NVR‐1620