"Spy-in-the-sky" technology, developed for military purposes, is being proposed by police for uses in crime prevention and traffic congestion. Remotely-piloted vehicles carry small television and film cameras and infra red sensors. Aerial pictures can be transmitted almost instantaneously to headquarters up to 200 kilometres away. Flight paths can be preset or controlled from a base by computer. They are one-twentieth the cost of a full-sized helicopter. The potential exists for abusive monitoring of citizens' activities.