TOKYO -- Sohgo Security Services, commonly known as Alsok, will roll out a service this month that can serve as a sentry by listening for drones around government buildings and other important sites.

     Tiny unmanned aerial vehicles fly under the radar. When they operate autonomously, there is not even a radio signal from a remote controller to detect. But the Tokyo company's new service is based on detecting sounds -- the spinning propellers serve as an audio fingerprint identifying every make of drone.

     The Japanese government is now pondering regulations to prevent any repeat of an incident in April when someone landed a tiny drone on the roof of the prime minister's office. But regulations alone cannot stop all malicious intent with drones, so Alsok expects its new security service will find use everywhere from factories and research facilities to nuclear power plants and hydrogen stations.

     For this service, Alsok will use U.S.-made audio sensors that can capture sounds within a radius of 150 meters. For a building the size of the prime minister's office, three of the sensors will be able to cover the entire area.

     When the audio sensors pick up sounds, the system checks a database of audio fingerprints to determine if a drone has approached and to identify the type of drone. For added precision, image sensors can capture the shape of the drone. A warning is then sent to security personnel.

     Alsok is still setting pricing, but a service using one audio sensor will cost around 200,000 yen to 300,000 yen ($1,700 to 2,500) a month, which is far cheaper than stationing guards around the clock.

(Nikkei)