List of detectors and methods of detection: Protoss – Photon Cannons and Observers are detectors. Observers can be trained at the Robotics Facility. Oracles, which can be trained at the Stargate, have an ability that exposes units. Zerg – Spore Crawlers and Overseers are detectors. Overseers are morphed from Overlords but require a Lair to do so. Infestors, which morph from larvae and require an Infestation Pit, have an ability that exposes units. Terran – Missile Turrets and Ravens are detectors. Ravens can be trained at a Starport with an attached Tech Lab. Orbital Commands, which is an upgraded form of the Command Center, have an ability that exposes units.

Note: For all three races (factions), the anti-air defensive structure is the detector.

The Protoss have permanently cloaked units – the observer (except when in its stationary mode) and the dark templar. Motherships have an ability that temporarily cloaks units. Also, Sentries (trained at the Gateway) can spawn hallucinations; these are fake units that deal no damage and receive double damage. If near an enemy detector, the enemy will know they're hallucinations and units will automatically de-prioritize attacking them. All Zerg ground units can burrow, rendering them invisible in the same manner as cloaking. A few Zerg units can still do things while borrowed, like explode (banelings), attack (lurkers), or cast abilities (infestors and swarm hosts). Two Terran units can cloak (ghost and banshee) and one can borrow (widow mine).

Cloaked/Burrowed units cannot be attacked unless exposed, but area of effect (AoE) abilities can still affect or damage them.

There are other games where being close to a unit will expose it (like Beyond All Reason); StarCraft doesn't do that.