Houston Mayor John Whitmire called SpotShotter's technology a "gimmick" and a "feel-good program" that law enforcement doesn't support amid discussions to end the city's contract.
Worcester officials approved the use of software that uses automated data analysis to direct when and where police patrols visit certain neighborhoods.
Speakers at a smart-cities conference outside Washington said their programs are only worthwhile if residents understand the new technologies being deployed in their communities.
The Fresno Police Department's ShotSpotter system will be extended to cover more than 14 square miles following a recent high-profile shooting in Florida.
The city has requested permission to operate the aircraft beyond visual line of sight, as allowed by an experimental "innovation zone" program started by the Trump administration.