The resequencer was a component used in transporters.
While discussing options to end the hostage situation at the Vulcan monastery at P'Jem in June of 2151, T'Pol mentioned that the transporter was no option because the sound alone would alert the guards and they would start firing before the assault team was fully resequenced. (ENT: "The Andorian Incident")
In 2153, while Commander Trip Tucker and Ensign Travis Mayweather were attempting to beam aboard some trellium ore from an asteroid field, a spatial anomaly caused an overload in the resequencer, which caused the asteroid to materialize in several pieces embedded in the transporter wall. (ENT: "Impulse")