San Francisco passed a similar ban earlier this spring. Somerville, Mass. implemented a ban last month, and the California legislature is considering a bill that would prohibit the tech in police body cameras. Even Axon, a major supplier of police body cameras and software, has said it will not include face-matching technology in its cameras -- at least not until it's more accurate.

While the Oakland Police department doesn't currently use facial recognition in its body cameras, Chief of Police Anne Kirkpatrick did advise against a complete ban. But Kaplan pointed to MIT research that found facial recognition systems had higher error rates when identifying females and minorities. Her letter also noted that Apple is being sued by an 18-year-old who alleges facial recognition led to his wrongful arrest and that facial recognition is being used to monitor ethnic minorities in China. While two of the three facial recognition bans are in California, there's a good chance restrictions like these will become more common throughout the country.