A homing transponder
A homing transponder was a piece of technology that dramatically enhances transporter effectiveness and range.
In 2375, a transponder was used to transport Kira Nerys multiple light years to Empok Nor. (DS9: "Covenant")
It is possible that Eris was wearing a transponder when she was beamed off the station in "The Jem'Hadar". Upon beaming out of the operations center, she left no trace or indication of where she had gone. It could also have been used by Dukat in "Tears of the Prophets" to go to the station and back into Dominion territory.