Rocket Sentry

The Rocket Sentry in Portal is almost an opposite to the Sentry Turret. Portal's turret sentries fire streams of bullets, speak in childish voices, and can be deactivated or picked up and moved by Chell. Rocket sentries fire one-hit-kill rockets, are fixed to the floor, are indestructible, and play a distinct lock-on sound rather than speaking. Although Chell encounters several turret sentries in the final few test chambers, the game features only two rocket sentries, both found in the abandoned portions of the Aperture Science Enrichment Center.

The rocket sentry's sensor, visible as a blue-green laser, moves slowly. After locking on, the sentry always pauses briefly and then fires a single rocket, even if the target has already moved. Because of this, Chell can "trick" rocket sentries into breaking inconvenient objects.