I haven't even used the two I ordered yet outside, but I tested them inside and powered them up with a portable power source that I connected via USB and they worked like a charm. According to other reviewers these deter some flies but not others. So we'll see what happens on my patio. They certainly can't hurt. They are silent, so that's good. And even though the included tea light and tea light porthole that's built into the device seem a bit corny, it's actually a nice dual feature!