Don't just watch the hands... examine them
Just because you don't see it, doesn't mean it's not there. I'm referring to a weapon in a subject’s hand.
Sometimes you approach a subject with tunnel vision — and that can be a big mistake — because you are looking through or around the subject instead of first noticing the placement or position of the hands.
You would be surprised to see how many weapons can be hidden, palmed, or held against the back of the forearm. When a subject crosses his or her arms, they can hold weapons out of sight.
Try it yourself. Take a knife any size up to hunter type and conceal it from view. Look in a mirror and see all the ways a weapon can be held by a subject and hidden from view. I have become a master at holding a knife out of plain sight. A smart officer will ask a subject to open his hands up, fingers spread apart and palms down, and let gravity take over. Of course, you always have to be careful of a firearm, which can be held in the same manner: out of sight, but ready to discharge.
Ladies and gentlemen, sometimes you have to think like a criminal to defeat one.
Be safe, always tactical.