OAK BROOK, Ill.  Six days a week, in fair weather and foul, two-dozen door-to-door salesmen, all of whom live clustered together in an apartment complex in this suburb west of Chicago, pile into S.U.V.’s and cars and head into the big city, bent on sales of home security systems.

And on Sunday, their one day off, they drive together to the nearest house of worship of the Church of Jesus Christ of Latter-day Saints.

The salesmen are mostly former Mormon missionaries from Utah who cut their teeth  and learned their people-skill chops  cold-calling for their faith. In Chicago and in its suburbs where their employer, Pinnacle Security of Orem, Utah, has shipped them for the summer sales season, they are doing much the same thing, but as a job.

“It’s missionary work turned into a business,” said Cameron Treu, 30, who served his mission in Chile and was recruited into D2D (that is door-to-door in sales lingo) by another former missionary.