While tens of millions of Americans watched Hillary Clinton and Donald Trump tear into each other during the final 2016 presidential debate Wednesday, law enforcement monitored the skies above the battleground for drones.

Security at any big national political event is always tight, but the tenor of this bitterly fought race has ratcheted up anxiety. So Las Vegas police hired specialists to set up a drone detection system around the University of Las Vegas venue.

They used Dedrone, which has technology that monitors airspace for unauthorized drones within a radius of several hundred meters from any given location.

A Las Vegas police spokesman confirmed that the system was in place Wednesday night. And, he said as far as he knew, no drones were detected. He added that UNLV is so close to McCarran International Airport that it was already a drone-free zone. But in the past, such details haven’t kept people from flying drones where they shouldn’t.

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Dedrone says that its customers include data centers, oil-and-gas facilities, prisons, and even Citi Field, home to the New York Mets. For the Las Vegas job, it worked with system integration partner AirVu to put the whole implementation together..

Dedrone’s technology is all about spotting and identifying wayward aircraft, not disabling them. That job typically goes to security people on the ground who try to locate any drone operators. Some companies offer drone-stopping services primarily for military and national security.

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San Francisco-based Dedrone is also working with aircraft manufacturing giant Airbus airbus-group-n-v to bring its drone detection to major airports, which need to have airspace that is free and clear of drone distractions and possible collisions. There have been hundreds of close calls near airports over the last year.

FAA rules bar drones from interfering with manned aircraft. Drone operators should notify the airport if they plan to fly within a five-mile radius.