Wailing Stone

The "Wailing Stone" is an artifact found by the Crystal Gems in the episode "Rose's Room". It appears that the Wailing Stone can only send audio, but is capable of receiving both audio and video (although it was not originally intended to receive the latter). It was used in the Rebellion, as confirmed by Pearl, to send messages back and forth.

Wailing Stones appear to have two significant parts: the "button" on top and its hole, which the audio plays out of.

The Wailing Stone's abilities can be augmented so that it can interpret messages that are normally too advanced by integrating it into a television.

"Rose's Room"
The Crystal Gems found the Wailing Stone on one of their missions in the Northern Hemisphere. When the stone is activated by pushing the button at the top, it emits a very loud, ear-piercing sound that causes objects to break, such as Steven's television screen.

"The Message"
Lapis Lazuli used advanced Gem technology to warn Steven of the Homeworld Gems' coming arrival to Earth on their hunt for him and the Crystal Gems. The Gems were unable to decipher the message until Greg converted it into video due to the Wailing Stone's abilities being limited to playing audio.

Trivia

 * The Crystal Gems have collected all known Wailing Stones on Earth.
 * Audio from a Wailing Stone cannot be muted, but it can be muffled ("The Message"). Attempting to turn it off failed, along with trying to bubble it.
 * Originally, the stones only played simple audio messages, but due to the technological advances at Homeworld (as stated by Lapis Lazuli in the "The Message"), the frequency couldn't be translated to audio, because it was video.
 * The sound effects for the Wailing Stone were made by Rebecca Sugar playing on a modified Omnichord, and Toy playing on effect pedals.
 * It has been shown that Wailing Stones can magnify the voices of humans and Gems, as unexpectedly demonstrated by Steven in "The Message".
 * The gold patterns on the Wailing Stone resemble typical designs for containing cabochons.

Cultural References

 * The Wailing Stone resembles the Standing Stones in Skyrim.

La Roca de los Lamentos