Why This Is a Companion Piece A few days ago I wrote Turn Your Old Android Phone Into a Free Security Camera (No Subscription Required) — a step-by-step guide to repurposing a drawer phone as a continuous-recording security camera with no cloud, no account, and no monthly fees. That post answered "how." This one answers "why it works at all." If you're an Android developer, the question that should be bothering you is: if a drawer phone is hardware-equivalent or hardware-superior to a $300 security camera, why doesn't every Android phone already do this? The answer is software, and it's interesting. The Three Things Stock Android Won't Do Out of the box, an Android phone is unusable as a security camera for three specific reasons: The camera surface is destroyed when the screen turns off. This is a battery decision, not a hardware limitation. The OS assumes that a user-facing app cannot be doing useful work when the display is off, so it tears down the Camera2 session. There is no built-in remote viewer.…