There's a nifty simple FOSS app called SOS Flashlight, that translates your text into Morse Code, to be flashed via flashlight, the screen, and/or emitted as beeps.
It would be neat if it could actually detect and decode the flashing codes from another device though.
I currently have the SOS Flashlight app set to emit Morse Code for this message from our sponsors...
"We have been trying to reach you regarding your vehicle's extended warranty."