noisebell/pi

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.