Sonic Invaders

As the name implies, what this game consists of amounts to an audio-only take on Space Invaders, although Sabotage might be a more apt point of reference. The player occupies a stationary gun emplacement which can fire in one of each of seven directions, controlled by keypad directions. Alien enemies approach, typically one or two at a time in early levels, and for reasons of plot cannot be seen. Instead, the player needs to be wearing a pair of stereo headphones to help determine, aurally, the enemies' angle and distance from the emplacement and which of the seven directions will be the one required to nail the bogey. Unlike some audiogames, the screen isn't entirely blacked out, but instead displays some instrumentation like a night-time flight simulator might -- indicating useful figures like the total number of currently active enemies and how much remaining time each of your seven cannons requires to reload.

It's a complicated situation. Different enemy types move and fire in different ways, and can be distinguished by the different noises they make. Compounding this, each of your guns needs time to reload before firing again. On the plus side, the player does have a shield at their disposal, though while it is raised one can't attack the invaders.

Each level is timed, counting down, and the player's goal is to hit as many enemies as they encounter (rather, to avoid being hit by any enemies -- in this fixed position, the best defense is a good offense). At a level's end statistics will be calculated, measuring accuracy.