The Autonomous Library is a device and system built by Simon Voltaire, the Master of Paris, to document what happened all over the city automatically and continuously. To date it has only been mentioned in Othar's Twitter, and not the main comic.
The libraryThe actual sensor net which feeds data into the recording scribing mechanism is unknown, but may relate to the Master's , which may be secretly integrated into every structure in Paris.
The Library's lobby is at street level, but the scribing engine, and collation and storage systems are secured underground, protected with reinforced building against vibration damage (earthquakes, very large clanks, bombs) and environmental variation (cold/heat/humidity). The scribing engine itself was built and supplied to persist for 1000 years, unmaintained and unmonitored. Othar describes visiting it and finding it still functioning in an otherwise long-destroyed and abandoned Paris.
There is an implication that the Library archives were for public access, which further suggests Master Voltaire may have either set recording parameters to exclude his and the city's security secrets, or he had trusted staff winnowing the records as they came off the scribing engine.
It may be related to The Incorruptible Republic of the Immortal Library of the Grand Architect.