My company, does random breathalizer testing. Mostly after lunch hour. We call in a crew and have them do their "cup thing" and take a breath test.
We also do it on Monday mornings before they begin work. If they show any reading, they are sent home immediately, without pay. They are class 2 drivers and also operate heavy equipment and work around high tension utilities.
It's amazing how many also get sent home the next day.

Safety first.