Chilling video shows how easy it is to miss signs of human trafficking

A video set in an idyllic town showing smiling service workers going about their jobs has a chilling twist in its tail.

How many signs of human trafficking did you miss when you watched?

The Michigan State Police created the film to alert plumbers, electricians, gardeners and other service workers that people may be held captive in the homes they visit.

Signs include barred windows, padlocked interior doors and people being hustled into vans and away from public view.

"You are on the front lines in homes and in neighbourhoods," Colonel Kriste Kibbey Etue, Director of the Michigan State Police, tells service workers in the film. 

"You can help save those who are being victimised."

Globally, there are 20.9 million victims of human trafficking, according to the nonprofit Polaris Project, in a multi-billion-dollar criminal industry.