Face tattoos, typically reserved for rappers and rockers, could one day be used to make sure everyday office workers aren’t overexerting themselves. “Now we have the ability to monitor mental strain, which hasn’t been tracked.”The new wearable was revealed this week in the journal Device. Enter electronic tattoos. Last year, the same team created a liquid electronic tattoo ink that could be sprayed onto a person’s scalp. It’s also unclear how others might respond to sitting shoulder-to-shoulder with a coworker covered in face sensors