Subspace transponder
A subspace transponder was a subspace communications device aboard starships used to locate and identify objects in space, such as other starships or shuttlecraft.

Each Starfleet starship sent out a unique subspace transponder signal. By comparing the signal sent from a moon of Mab-Bu VI with stored transponders signals from other starships, Data was able to identify the distress signal as originating from the  starship . ()

While searching for the mission recorder of the Klingon  attack cruiser  near Deep Space 9, Chief Miles O'Brien detected the weak subspace transponder signal from the recorder. ()

Captain Kathryn Janeway gave the Vhnori Ptera a subspace transponder before beaming her into a subspace vacuole where she should give the transponder to Harry Kim. ()

The Doctor implanted a transponder in Neelix and Chakotay's palms before they infiltrated Quarra. It allowed them to maintain an open communications link and transport them through the   shield grid. ()

Subspace
Communications technology