NEC has developed a surveillance system that can spot drones from up to a kilometer away. The system is intended to be used around places like sports stadiums, nuclear power stations and government buildings, and can detect drones in several ways.

At the heart of the system are two cameras: an ultra-sensitive camera that sees in the visible part of the spectrum and an infrared camera.

But it also includes acoustic sensors that can listen for the sounds made by drones, and a radio detection finder that first attempts to identify drone communication signals and then uses triangulation to determine a location.

Martyn Williams The monitoring screens of a drone tracking system developed by NEC and on show at Ceatec in Japan on Oct. 6, 2015.

The range of each of the sensors differs, but the visible light camera is said to be good to up to 1 kilometer, the thermal camera up to 120 meters, acoustic sensors to 100 meters and the radio detection finding to 1 km.

Together, the sensors search for drones and when one is spotted will alert operators to its presence.

In many countries, the illegal flight of drones is becoming an issue as the price of the devices gets cheaper and their popularity increases.

In Japan, a hobby drone with trace amounts of radiation recently crashed on the roof of the prime minister's office in central Tokyo. In January this year, a drone taken on a late-night flight by a government worker crashed onto the White House lawn. The U.K. recently secured what police called their first prosecution against a drone operator for flying over football stadiums.