This article is from the Baby Proofing FAQ, by Sandra Smith, firstname.lastname@example.org with numerous contributions by others.
From: Cynthia L Macaluso
I just wanted to add a point about household sewing machines. I often
leave my sewing machine set up in my sewing room. The man who fixes my
machine told me recently that when he was a child, he "sewed" the needle of
his mother's sewing machine through the palm of his hand. He recommends
ALWAYS pulling out the clutch (the turny wheel part on the side that you
pull out when you want to wind a bobbin and not have the needle go up and
down)when leaving the machine, even to answer the phone. Unplugging it
doesn't necessarily work; my kids (2 and 3 yrs) have plugged mine
in...but they haven't figured out how to push in the clutch yet!
Without the clutch pushed in they can't make the needle go up and down.