The problem, such companies say, is that regulations on the use of drones - and about countering them - are still in their infancy. In countries like the United States and Australia, for example, drones are considered private property, and they can only be jammed by government agencies.

"Mitigation capabilities," says Jonathan Hunter, CEO of Department 13, "are therefore limited."

Oleg Vornik, chief financial officer of DroneShield, however, says: "This is expected to change shortly as governments start to recognise that critical infrastructure facilities such as airports need to be able to defend themselves against drones."

In the United States, the Federal Aviation Administration is testing various counter-drone technologies at several airports.

Interest in the space will only grow.

London will next year host the world's first two conferences on counter-drone technologies, says Jenzen-Jones. But there will also likely be consolidation.

DroneShield's Vornik says the company has counted 100 counter-drone start-ups, and is talking to more than a dozen of them as potential acquisition targets.

It's too early, Vornik says, to see evidence of moves to get around anti-drone technology. But Amazon.com last month tested deliveries in the UK via drones, and published a patent describing how it might defend drones from threats, ranging from a bow and arrow to signal jammers.