Don't think you are always safe even when plugged in at home. I am on my winter home base now and a few weeks ago my Progressive unit shut my power off at 3:00am. I didn't think much about it because it was back on when I got up later. The next morning at the same time it did it again. Then I went out to look at the code. It was high voltage. It seems Alabama Power had a transformer failing. They replaced it a few hours later and no problem since.
My home base is a lot in a residential area and no one uses my power pedestal but me. The only other users on the same transformer as my site are s&b and I'll bet none of them knew they had high voltage (over 132 volts) unless they had some light bulbs fail.