The first signal arrived as a door.
Not a metaphor. A black service door in a rented hallway between two offices that had both been vacant for years. The building directory listed a dentist, a freight broker, and a language school that no longer answered its phone. No fourth tenant. No basement. No room behind the door on the floor plan.
The door had no handle.
It had a brass plate where the handle should have been. On the plate: a shallow cut, not quite a circle, not quite an eye. Under the right light it resembled a sigil. Under bad light it resembled a mistake.
Procedure
We recorded nine knocks.
Three from member one. Three from member two. Three from member three.
The first six returned no echo. The final three returned something like a room tone, but reversed: not a sound inside the recording, a pressure around it. When the file was opened in the editor, the waveform showed a clean block of silence where the last knock should have been.
Silence is easy to fake. The response was not.
After export, the file name had changed itself from door.wav to door.remembers.wav. The filesystem timestamp predated the recording session by forty-one minutes.
Result
We erased the file.
The mark on the brass plate darkened after deletion.
No further contact was attempted. The building was demolished six weeks later. The lot is still empty.
Note
A door that opens is architecture.
A door that remembers is an index.