[Aris_Sung]

Here's a suggestion: A sensor technology that is capable of detecting from types of planets to ship movements (depending on what model and so forth). It would be heavy so, it would take up most of the space on a satellite or some of the space on a ship.

For races that are not telepathic, there can be a facility called 'observatory' which can detect ships within so many sectors and is basically a sensor for planets.