The world's longest undefended border will soon have eyes in the sky. US Officials say a robot-controlled surveillance aircraft will start patrolling part of the Canadian border by the fall. US Customs and Border Protection says the propeller-driven drones called Predators will be launched into American airspace, and will fly day and night between North Dakota and Manitoba and Saskatchewan. A Predator can cover about 1,400 kilometres in a five-hour mission and can remain airborne for up to 36 hours.