How to capture intercom button press event in plugin DLL via Metadata SDK (SDK 5.1.3)

I'm working on a plugin DLL using the NX Meta Plugin SDK (version 5.1.3) and I need help capturing events from an intercom device (Hanwah TID-600R device).

Currently, I'm successfully detecting motion events by checking for IMetadataPacket with motion metadata, and then triggering a 10-second video download using DeviceAgent::pushUncompressedVideoFrame.

Now I’d like to do something similar for an intercom button press—specifically, when someone presses the call button on the intercom device, I want to capture that event and start recording.

My question is:

• Is it possible to detect a button press event from an intercom device using the Metadata SDK?
• If so, how can I receive that event in my plugin DLL?
• Is there a specific metadata type or event packet I should be listening for from the VMS?

Any guidance or examples would be greatly appreciated.

I would like to capture this event exactly in my plugin .I can very well see the event in vms when Proximity sensor is triggered and can hear bell sound .so need to know is it possible to capture this event when trigger 
is it possibleto use any of the code from this git
https://github.com/networkoptix/nx_open_integrations/tree/master/cpp/vms_server_plugins/opencv_object_detection_analytics_plugin