The Game Boy Pocket Sonar was a legitimate Game Boy accessory that you could actually use to find fish underwater. This was not a joke or an April Fools prank—it really worked.

Made by Bandai, the Pocket Sonar was only available in Japan, which was a shame, because it would have been perfect for all those fishing trips where you forgot your sonar but brought your Game Boy with you. It even had a fishing mini-game built in for when you inevitably got bored of actually fishing.