Police have started using live facial recognition in Stevenage town centre.
The technology aims to find wanted offenders and protect vulnerable people.
It works by comparing live camera footage of faces to a pre-set watchlist, alerting officers if a match is found.
Police believe live facial recognition is an effective tool for preventing and detecting crime.
They said they acknowledge the need to balance privacy concerns with protection, and are aware of the technology's legal and ethical implications.
In a statement, Herts police said: "We will be open and transparent in the development, deployment and use of live facial recognition technology, recognising that we must retain the confidence of our communities as we trial this new and important crime-fighting tool."