Radio Defense Game

Raiders are coming in, and only Command can see them. Command reads their grid coordinates over the radio, such as B7, D2, F5, and then the radar goes dark. Tap the cells in the order you heard them before the raiders arrive. Every round that you clear adds one more coordinate to remember.

How to play

1. Choose how the orders reach you. On RADIO, a voice reads them out in the radio alphabet, such as Bravo 7, and nothing shows on screen. On TELETYPE, each coordinate prints on a paper strip and blanks out when the next one comes.
2. Command reads one coordinate every 1.5 seconds in round 1. When the last one is read, the radio goes quiet and the radar goes dark.
3. Tap the cells in the same order. Each tap is checked against the coordinate in the same place on the list, so the right cells in the wrong order still miss. There is no time limit in the dark.
4. After your last tap the radar lights up. Raiders you tapped burst, and any you missed get through and cost a life. Three lives lost end the game.

The first round has 3 coordinates. A round with no misses adds one, up to 12. A missed round keeps the same number, and two missed rounds in a row take one away, never going below 3. The pace also quickens by 0.05 seconds a round, until Command reads one coordinate a second from round 11 on.

The columns run from A to H across the top and the rows from 1 to 8 down the side, with 1 at the top, as in a spreadsheet. On a keyboard, type a letter and then a number, such as B then 7, to tap a cell. You can also move around the radar with the arrow keys and press Enter. Backspace undoes your last tap, and Escape pauses. Pausing cuts the radio off, and when you resume, Command repeats the coordinate it was reading.

RADIO uses only voices that your browser reports as built into your device, and the game never sends the coordinates anywhere itself. If your browser has no such voice in English, RADIO is greyed out and you can play on TELETYPE instead. Starting a game on RADIO turns sound on, unless you have turned sound off yourself. Then the game stays quiet, with a note saying so, until you press the sound button. That button mutes the voice along with the game's other sounds.

Scoring

Each raider you hit scores 100. A round with no misses scores a bonus of 50 for each of its coordinates, so a clean round of 3 scores 450 and a clean round of 5 scores 750. A round of 5 with one miss scores 400 and costs a life.

• RADIO and TELETYPE keep separate high scores, because hearing a list and reading one are different tests.
• Your five best scores for each are saved in this browser, with the round each game reached. The game over screen also shows the longest sequence you cleared.
• In practice, no lives are lost, the pace stays at 1.5 seconds, and RADIO shows each coordinate as a caption while it is read. End a practice game from the pause screen. Practice games are not saved.

About memory span

Radio Defense is a memory span test with a story around it. Psychologists have measured span since the 1880s by reading out a list of digits and asking for it back in order, a test now called digit span. Its spatial cousin, the Corsi block-tapping test, has the tester tap a row of blocks and the subject tap them back. Here each item is a grid cell, which pairs a letter with a number and a place on the radar.

Memory competitions have a spoken numbers event, in which digits are read aloud at one a second and recalled in order. Competitors handle it the way strong Radio Defense players will. They turn each item into a picture, for example with the Major System, and place the pictures along a short route in a memory palace. Another way is to picture the cells as a path drawn across the radar.

Read about memory competitions, learn how to memorize numbers in a memory palace, or try our other free memory games.