On Probe Detection

Espionage Centers are no guarantee that probes will be detected, but they help.

In an experiment, 20 probes were sent to planets with strong defenses and level 5 Espionage Centers. Half (10) got through and half were detected and shot down.

20 probes were sent to planets with no defenses or Espionage Centers. 80% (16) got through. 20% (4) were detected and shot down.

The more probes that are used (up to 5), the more information comes back. In this test, each probe was actually a batch of 5 probes. So the ones that got through brought back full information about the planet.

So even with a level 5 Espionage Center, you may well be probed without your knowledge.

A side note: The probes bring back a count of the ships defending the planet, but not the class or type of ships. So having 1200 level 1 ships on defense won't do much against an attack, but they might well deter one.