This seems to be the best method for detecting moments of engagement or disengagement. Is there currently a way to do this with PM, or would a custom action be needed?
VREvent_TrackedDeviceUserInteractionStarted
VREvent_TrackedDeviceUserInteractionEnded
There is also:
In Unity using the OpenVR plugin, the function to check is: OpenVR.System.GetTrackedDeviceActivityLevel(0)