Setry Sleepiness Prevention system

I want to detect a sleeping sentry in guard room or post(if they are stationary for more than 30-45 sec while standing or sitting as only face detection will not be helpful as they wear helmet or mask. Avoid eye, ear and mouth detection as sentries may also face the other way and dont always look at camera.) The data input should be from a video stream from cctv/webcam. an alarm generation should be possible.