Police officers in Potters Bar are being trained to use lie-detectors as part of a campaign to target sex offenders.
Hertfordshire Police are joining detectives in South Yorkshire training to use polygraphs.
The 11-week course, which began earlier this month, is the first of its kind for British policing.
Professor Don Grubin has been working closely with Hertfordshire Constabulary for a number of years to explore new ways to manage the risk posed by sex offenders.
In particular, he focuses on those who have been arrested for possession of indecent images of children.
The results of the initial work showed that polygraph testing, when used as part of the risk assessment process, helped officers gather new information.
Detective Chief Inspector Stuart Orton, who leads for the force on protecting vulnerable people has been involved in leading the polygraph testing work for Hertfordshire.
He said: “The polygraph testing is not about sex offenders confessing their crimes, it is about assessing the risk they pose to the community and in some cases themselves.
“It’s a measure used with other investigative tools by specialist officers in our child online safeguarding team to protect the public.”