Previously, previously, previously, previously.
Link in the post is corrupted. It's here.
You can find more of this stuff on his twitter: @_MG_
I love the name. It looks like the creator is a NIN fan also -- his Twitter profile describes him as "just some flesh caught in this big broken machine".
In the Medium post, he also hypothesises a "sound grenade":
When plugged in, the keystroke injection does whatever you wish, then a loud siren would trigger that cannot be turned off until the battery dies.
He should call that one "Screaming Slave".
Tossing the innards of a musical greeting card somewhere inaccessible is the obvious prior art here.