Clearance in Control Resonant is broken up by different levels, each of which requires an associated keycard. Some levels of Clearance are accessible as part of the main story, while others are found as part of optional side quests in which different levels of clearance are required to progress. The reality is that you probably encountered several doors that require clearance that you don't have during the tutorial where you escape from the Oldest House, but while you couldn't open them the first time around, you can come back later with the keycards and see what you find beyond.

There are 5 Clearance Keycards players can obtain in Control Resonant, all of which open different doors in different locations.

Across Control Resonant you'll occasionally encounter doors with a Clearance Level 18 requirement. However, at no point in the game is Dylan given a Keycard that allows him to open these doors. On the occasion that one is opened, it's always done so by an NPC who has their own clearance, and it seems as though some doors with Level 18 are never opened at all.

Control Resonant Taxi locations: Find all the Taxis and solve their puzzles
Control Resonant Mysterious Dog locations: Discover the dog in every zone
Control Resonant Camera and Instant Photo locations: Track the Freeze Frame camera through Manhattan

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