User blog comment:The Milkman/Indoctrination Theorists Say the Darndest Things/@comment-4941068-20121023181702/@comment-24174486-20121023220447

"Usually, you can spot a deus ex machina if it's sole purpose in the plot is to resolve the conflict."

That would describe a plot device. While a plot device can be a deus ex machina and vice versa, it is not invariably so.