Telemetry probe

A telemetry probe is a device used utilised by the UNSC.

Overview
The only known usage of these devices was to attach it to a Covenant ship and track it through slipspace. In 2537, at the Battle of New Harmony, the prowler managed to attach one to a Covenant warship at the battle, and track it to K7-49, a Covenant shipyard facility seventeen light years from the UNSC outer colonies.

Because the Covenant are imitative, not innovative, it can be conjectured that the Covenant spy probes used to find the location of Reach by attaching it to the destroyer was based upon this technology, discovering it then reverse engineering it to make the spy probe.