I think anyone who's used a lawnmower knows the concept but not necessarily the name.
And most people aren't electric lawnmower users anyway.
All powered lawnmowers have these switches. Push types have the spring loaded lever on the handle that shuts the engine off when released, and riding mowers shut down when there isn't weight on the seat. This isn't exclusive to electric mowers at all.
i've used a lawn mower many many times and there is no part of it I would have called a "dead mans switch". I'm sure it's technically there, but knowing the name is hardly a requirement. Also, i'm certain there is not a 1:1 overlap between abuse victims and lawn mower users.
Know the functionality, but how should you guess the term from operating a lawn mower?
So obviously "Dead Man's Switch" is a smart lawnmower remote control app.