My son in law has a small drone with a camera and we used it a few months ago along the river. Almost impossible to spot at low level and only really visible high up in clear sky and only IF you're really looking for it. He used it to follow my daughter and I and he was 1/2 a mile away and following us at about 20 feet up, we didn't know. Even then it was a scary/wierd scenario and he wasn't trying to kill us with it ( showed us the film ). Those things loaded with munitions , as seen, would be fucking brutal.