Morse as light

The screen flashes your message at proper morse timing. It costs nothing to run and works when sound will not carry.

Light carries where sound does not

Signalling by light is the oldest practical use of morse and still the most useful one to have in a pocket: across water, across a valley, or through a window. The timing is identical to audible morse — only the medium changes.

Contrast matters more than brightness

A screen flashing white on black is legible much further away than one flashing a mid tone, because the eye reads the transition rather than the level. Keep the background as dark as the display allows.

Questions

What is SOS in morse code?

Three dots, three dashes, three dots — ... --- ... — and it is sent as ONE symbol with no gaps between the letters, which is why it is written <SOS> rather than S O S. It was chosen because it is unmistakable and easy to send, not because it stands for anything; "save our souls" was invented afterwards.

How fast is 20 words per minute?

A dit is 1200 divided by the speed in words per minute, so at 20 WPM a dit is 60 milliseconds and a dah is 180. The standard word is PARIS because it is exactly 50 units long, which is what makes words per minute a precise measure of morse rather than an approximate one.