How to get an event or a callback from camera when its alarm input is triggered?

Hi,

I connect my IP camera HIK DS-2CD3145F-IS to external motion detector. In WEB->Configuration->Event->AlarmStatus, I see Alarm status “On” by motion. I can get this status through ISAPI too: ISAPI/System/IO/outputs/1/trigger. Now my question – how I can get event or set callback by change alarm status? I don’t want ask the camera alarm status every second but I need camera event if status changed.