Dot Dash

Signal probes fall toward a radio dish in a city at night, and each one sends a letter in Morse code: written on its tag in dots and dashes, and blinked on the lamp on its aerial. The lowest probe is the target, and it beeps its letter. Under the dish are six chambers that each hold a rocket and a letter. Tap the chamber with the letter the target sends, and its rocket is loaded and fired. The letters change chambers every wave, so you learn the sound and not the button.

How to play

1. Choose a mode: letters, ear only or numbers.
2. Each wave puts six letters in the chambers. A wave with new letters first sends each of them once, written in the sky beside its code.
3. The lowest probe is the target, with a ring round it, and it beeps its letter. Tap another probe to aim at it instead. Tap the target, or press R, to hear it again.
4. Tap the chamber with the target's letter. Its rocket is loaded and fired, and the right one destroys the probe.
5. A wrong letter fizzles. The probe drops a step, the launcher jams for a moment and says Jammed, the right letter shows under the probe, and its code is sent again.

The game is built round its beeps, so turn sound on. Like every arcade game on the site, it starts with sound off, and its start screen has a button that turns sound on. Letters and numbers can be played without sound, from the dots and dashes on the tags. Ear only cannot: it writes no code on the tags, so you read every letter by sound alone.

The first wave sends the six letters with the shortest codes: E, T, A, N, I and M. Each wave after it adds four new letters, the codes of three parts first and then those of four, until the whole alphabet is in play by the sixth wave. Numbers adds the ten digits after the letters. Then come words of two and three letters, such as THE and YES, one word to a chamber. Letters you got wrong, or that landed, come back with the letters in new places.

A wave has more probes than chambers, 7 in the first wave and up to 12 later, so a letter falls more than once and no chamber can be ruled out. A probe takes 14 seconds to reach the ground in the first wave and a little less in each wave after it, down to 8 seconds.

When the game ends, the game over screen lists every letter or word you got wrong or that landed, each beside its code, with what you picked instead, so you can go over them before you play again.

You have three shields, and a probe that reaches the ground costs one. On a keyboard, press 1 to 6 for the chambers as they are numbered, the left and right arrows to change the target, and R to hear the target again. Escape or Space pauses.

Scoring

The sooner you know the answer, the more a probe is worth.

• A probe destroyed with no wrong shot scores 100, plus up to 100 more for how high it still is.
• A probe destroyed after a wrong shot showed its answer scores 20.
• A wave with no wrong shot and no landing adds 250.

Your five best scores for each mode are saved in this browser, with the wave each game reached. In practice, a probe that lands costs no shield, so the game goes on until you end it from the pause screen. Practice games are not saved.

How the code is sent

Dot Dash sends international Morse code, the 26 letters and the 10 digits as the International Telecommunication Union sets them out. Each letter is sent at 20 words a minute, so a dot lasts 60 milliseconds and a dash three times as long, with longer gaps between the letters of a word. This is Farnsworth timing, a common way to teach the code: each letter is heard at full speed as one sound, a rhythm to know, rather than a row of dots and dashes to count, and the gaps leave time to name it before the next.

How to remember Morse code

Learn each letter as a sound rather than a picture of dots and dashes. A common way is to say the sound aloud, "di" for a dot and "dah" for a dash, so A is di-dah and N is dah-dit. The code gives the shortest sounds to common letters, such as E and T, so the game starts with the short codes and builds the longer ones from them. For a letter that will not stick, make an image that links its sound to the letter. See how to create mnemonic images for ways to build one. The letters listed on the game over screen are the ones worth making an image for first.

Try our other free memory games, such as Radio Defense, which also trains your ear, or Star Charts for the constellations.