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Monitors sound, movement, vibration, ambient light, charger state and whether the device has been picked up. Correlates them into one incident, captures photographs and audio, encrypts everything on the device, and alerts you over Signal. Ask its status, arm or disarm it, retune its sensors or record the room, all over Signal, from accounts you approved on the device.
Leave-behind room monitor. Encrypted evidence, alerts over Signal.
Source Code available on GitHub https://github.com/AlsatianConsulting/sanctum Sanctum turns a spare Android phone into a leave-behind sentry. You put the device in a room, arm it, and walk away. When something disturbs the room, Sanctum records what happened, encrypts it on the device, and sends you a Signal message saying what tripped and when. It is built for the person who needs to know whether a room was entered while they were not in it. Its governing rule is that it never claims to be watching when it is not. WHAT IT WATCHES Six sensors, each independently switchable, each with a trigger line you set yourself against a live meter: • Sound, in dBFS against a baseline calibrated to the room • Movement, when the device is moved or tilted • Vibration, sustained — footsteps, a door • Ambient light, when the level changes • Power, when the charger is connected or disconnected • Picked up, when the device is lifted from flat, however slowly Several sensors firing at once is one incident, not six. A door opening changes the light, vibrates the table and makes a noise; Sanctum correlates those into one event naming every sensor that contributed. WHAT IT RECORDS Photographs from both cameras, audio when the sound sensor trips, and optionally video. Everything is encrypted with a key held in the phone's hardware keystore before it is written, never after. The incident database is SQLCipher. Deleting an incident destroys the key protecting its evidence, so deletion is cryptographic. Sanctum makes no claim that bytes are overwritten on flash. HOW IT TELLS YOU Alerts go out over Signal from a dedicated account on the device, end-to-end encrypted, to people you nominate. The message goes first and says what tripped. Photographs follow if you have asked for them. Audio and video stay on the device unless you ask for them by name. You can also instruct it over Signal from anywhere: ask its status, arm or disarm it, switch sensors on and off, move trigger lines, or record the room for a fixed length and have the clip sent back. Only accounts you have approved in person, on the device, are obeyed. Everyone else is met with silence rather than a refusal — a reply of any kind would confirm the number belongs to a device that is listening. No command destroys anything. An attacker holding an approved phone can stop it watching, loudly audited, but cannot erase what it already saw. IT SAYS WHEN IT STOPS A reboot, an upgrade, a force-stop, a revoked permission — anything that stops monitoring produces a message saying so. A monitor that goes quiet without saying so is the failure this application exists to avoid. Sanctum never claims uninterrupted operation. WHAT IT DOES NOT DO • No account, no cloud, no server, no telemetry, no analytics • No Google Play Services, Firebase or FCM — the build fails if one appears • No logging: there are no logcat calls in the app at all • No covert mode. Monitoring always runs a visible foreground service with an ongoing notification, and always trips Android's camera and microphone privacy indicators. This will not be made optional • No face recognition, person identification, or behavioural profiling • No SMS fallback. If Signal cannot deliver, the alert queues rather than downgrading to an unencrypted channel WHAT YOU NEED A phone running Android 8.0 or later, dedicated to this if you can. A phone number the device can receive an SMS or voice call on: it becomes the device's own Signal account and is signed out of Signal everywhere else. A second phone with Signal to receive alerts. Signal's registration challenge must be solved by a person. Free software under AGPL-3.0-only, drawing on Haven (Guardian Project) and on Molly and Signal-Android. Not affiliated with Signal Messenger LLC, the Molly project, the Guardian Project, or Google. Alerts are indicators that a sensor threshold was crossed. They are not proof of an event, and not proof of who caused it.