A targeting sensor is a sensor that is worn over the eye, allowing a person to see through solid surfaces. They can be exographic or exogenic.
In 2375, Chu'lak used an exographic targeting sensor to view his targets aboard Deep Space 9 before using a TR-116 rifle with a Micro-transporter to shoot them. Miles O'Brien later did the same during the investigation into how the killer was murdering his victims. Ezri Dax wore it while trying to get into the killers mindset and later to stop Chu'lak from killing her. (DS9 episode: "Field of Fire")
By 2379, TR-116 rifles used exogenic targeting sensors as a standard attachment. They were used by the crew of the USS Enterprise against the Tezwans during their peacekeeping duties on Tezwa. (TNG novel: A Time to Heal)