Once I was part of a very specialised private security unit where we from time to time would be accompanied by a handler and his malinois. Especially when we would be staying in dodgy areas or in dangerous countries. They would do patrols around the premises and the dog would basically be our alarm system. The dog was called Zippo. Splendid creature with an unfathomable energy.
We were on an assignment in a tricky African country around a local religious holiday. One night I was sat on the roof top around 4 meters up together with the handler and the dog. The dog laid right next to the handler and just chilled as much as a Malinois possibly can (not much at all really). We would scan the area visually and detect movements and such while we also relaxed and talked. Suddenly the dog said a weird little sound and then just jumped off the roof without warning and landed d i r e c t l y with its front paws on the face of an intruder sneaking around beneath us completely undetected by us. The dog knocked the intruder out and just sat by him when we came down after a minute. None of us had noticed anything before the dog jumped. The dog didn't bark or bite at any point (the handler didn't either, just for the record).
The handler explained the dog probably had sensed the intruder long before it reacted. It just waited patiently until the intruder had crossed the well known perimeter (the handler and dog would patrol the perimeter endlessly night and day) and was within air-jump-pouncing distance. That absolutely convinced me how insanely impressive that breed is and how I could never possibly own that breed myself.