Master Resonator

The Master Resonator was a piece of technology that was created by the Iconian civilization and had the capacity to shut down their gateway network.

At some point in their past, the scattered Iconian Empire deposited the Master Resonator on one of the worlds they had visited where it was held by a native primitive species. In 2376, the Sentries agreed to help Starfleet Captain Jean-Luc Picard to shut down the gateway network which had been activated by the Petraw and was causing havoc across the galaxy. However, their records informed them that they could only do this with the resonator and dispatched Picard to the planet in order to recover it. (SS TNG (The Other Side))