A towed pinger locator is a device towed (dragged)on a long line by a ship in order to locate the "ping" (sound) from a black box at the bottom of the sea.

Link to present incidents:
Defence vessel Ocean Shield acquired a signal twice, once for more than two hours, said Air Chief Marshal Angus Houston, who is leading the search.The signals were detected using the towed pinger locator deployed on the Ocean Shield.