Clients, the start-up companies say, range from intelligence agencies to hotels. DroneVision, for example, helped local police down 40 drones flying around Taipei 101, one of the world's tallest buildings and a magnet for drone users, in a single day.

In the Middle East, upscale hotels are talking to at least two companies about blocking drones from taking shots of their celebrity guests longing poolside or in the privacy of their bathrooms.

And even while the military, Jenzen-Jones says, may have the capability to bring down drones, demand is shifting to nimbler, more agile devices to cope with attacks using smaller off-the-shelf devices. "The key is looking for systems that are scalable, lightweight and easily deployable," he said.

DroneShield, an Australian-listed company, says it has sold its drone detection equipment to an Asian national security agency it declined to identify, and the Turkish prime minister's office.