The Warp Whistle is a musical instrument shaped like a flute. It can remotely activate Warp Pads when played. It resembles a recorder and is printed with diagonal blue, light blue and white stripes. It was first and so far only shown in "House Guest" where Greg uses it incessantly for unimportant reasons.
When Greg broke his leg protecting Steven and Connie in "Ocean Gem", Steven allows his dad move into the Beach House until his leg heals and his van is repaired. Before the Crystal Gems go and try to fix the Geode, Pearl lends Greg the Warp Whistle so in case if anything happens, he will just have to blow in it, thus activating the Warp Pad, alerting the Gems that they need to return. Greg uses it multiple times for unnecessary reasons and uses it to go to the Geode to fix it when trying to make amends for lying. It is unknown where the Warp Whistle is after the events of "House Guest".
- Even though humans have not been shown to travel or use Warp Pads alone, they can use the whistle to travel through or activate them, as Greg did to warp to and repair the Geode with his son Steven's help.