noisebell

Monitors a GPIO pin on a Raspberry Pi to detect door open/close events. State changes get POSTed to a webhook endpoint. Current state is available over HTTP.

Runs on NixOS with Tailscale for networking and agenix for secrets.

Setup

1. Hardware config

Replace hardware-configuration.nix with the output of nixos-generate-config --show-hardware-config on your Pi (or use an appropriate hardware module like sd-card/sd-image-aarch64.nix).

2. SSH key

Add your SSH public key to configuration.nix:

users.users.root.openssh.authorizedKeys.keys = [
  "ssh-ed25519 AAAA..."
];

3. Secrets

Get your Pi's SSH host public key and put it in secrets/secrets.nix:

ssh-keyscan <pi-ip> | grep ed25519

Then create the encrypted secret files:

cd secrets
agenix -e endpoint-url.age      # paste webhook URL
agenix -e tailscale-auth-key.age # paste Tailscale auth key

4. Deploy

nix build .#nixosConfigurations.pi.config.system.build.toplevel
nixos-rebuild switch --flake .#pi --target-host root@noisebell

Configuration

Options under services.noisebell in flake.nix:

Option	Default	Description
`gpioPin`	17	GPIO pin to monitor
`debounceSecs`	5	Debounce delay
`port`	8080	HTTP status port
`retryAttempts`	3	Webhook retry count
`retryBaseDelaySecs`	1	Base delay for exponential backoff
`httpTimeoutSecs`	10	Timeout for outbound webhook requests
`bindAddress`	`0.0.0.0`	Address to bind the HTTP server to
`activeLow`	`true`	Whether low GPIO level means open (depends on wiring)
`restartDelaySecs`	5	Seconds before systemd restarts on failure

API

GET / — current door state:

{"status": "open", "timestamp": 1710000000}

State changes (and initial state on startup) are POSTed to the configured endpoint in the same format.

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