---
sidebar_position: 6
title: "Signal"
description: "Set up Hermes Agent as a Signal messenger bot via signal-cli daemon"
---

# Signal Setup

Hermes connects to Signal through the [signal-cli](https://github.com/AsamK/signal-cli) daemon running in HTTP mode. The adapter streams messages in real-time via SSE (Server-Sent Events) and sends responses via JSON-RPC.

Signal is the most privacy-focused mainstream messenger — end-to-end encrypted by default, open-source protocol, minimal metadata collection. This makes it ideal for security-sensitive agent workflows.

:::info No New Python Dependencies
The Signal adapter uses `httpx` (already a core Hermes dependency) for all communication. No additional Python packages are required. You just need signal-cli installed externally.
:::

---

## Prerequisites

- **signal-cli** — Java-based Signal client ([GitHub](https://github.com/AsamK/signal-cli))
- **Java 17+** runtime — required by signal-cli
- **A phone number** with Signal installed (for linking as a secondary device)

### Installing signal-cli

```bash
# macOS
brew install signal-cli

# Linux (download latest release)
VERSION=$(curl -Ls -o /dev/null -w %{url_effective} \
  https://github.com/AsamK/signal-cli/releases/latest | sed 's/^.*\/v//')
curl -L -O "https://github.com/AsamK/signal-cli/releases/download/v${VERSION}/signal-cli-${VERSION}.tar.gz"
sudo tar xf "signal-cli-${VERSION}.tar.gz" -C /opt
sudo ln -sf "/opt/signal-cli-${VERSION}/bin/signal-cli" /usr/local/bin/
```

:::caution
signal-cli is **not** in apt or snap repositories. The Linux install above downloads directly from [GitHub releases](https://github.com/AsamK/signal-cli/releases).
:::

---

## Step 1: Link Your Signal Account

Signal-cli works as a **linked device** — like WhatsApp Web, but for Signal. Your phone stays the primary device.

```bash
# Generate a linking URI (displays a QR code or link)
signal-cli link -n "HermesAgent"
```

1. Open **Signal** on your phone
2. Go to **Settings → Linked Devices**
3. Tap **Link New Device**
4. Scan the QR code or enter the URI

---

## Step 2: Start the signal-cli Daemon

```bash
# Replace +1234567890 with your Signal phone number (E.164 format)
signal-cli --account +1234567890 daemon --http 127.0.0.1:8080
```

:::tip
Keep this running in the background. You can use `systemd`, `tmux`, `screen`, or run it as a service.
:::

Verify it's running:

```bash
curl http://127.0.0.1:8080/api/v1/check
# Should return: {"versions":{"signal-cli":...}}
```

---

## Step 3: Configure Hermes

The easiest way:

```bash
hermes gateway setup
```

Select **Signal** from the platform menu. The wizard will:

1. Check if signal-cli is installed
2. Prompt for the HTTP URL (default: `http://127.0.0.1:8080`)
3. Test connectivity to the daemon
4. Ask for your account phone number
5. Configure allowed users and access policies

### Manual Configuration

Add to `~/.hermes/.env`:

```bash
# Required
SIGNAL_HTTP_URL=http://127.0.0.1:8080
SIGNAL_ACCOUNT=+1234567890

# Security (recommended)
SIGNAL_ALLOWED_USERS=+1234567890,+0987654321    # Comma-separated E.164 numbers or UUIDs

# Optional
SIGNAL_GROUP_ALLOWED_USERS=groupId1,groupId2     # Enable groups (omit to disable, * for all)
SIGNAL_HOME_CHANNEL=+1234567890                  # Default delivery target for cron jobs
```

Then start the gateway:

```bash
hermes gateway              # Foreground
hermes gateway install      # Install as a user service
sudo hermes gateway install --system   # Linux only: boot-time system service
```

---

## Access Control

### DM Access

DM access follows the same pattern as all other Hermes platforms:

1. **`SIGNAL_ALLOWED_USERS` set** → only those users can message
2. **No allowlist set** → unknown users get a DM pairing code (approve via `hermes pairing approve signal CODE`)
3. **`SIGNAL_ALLOW_ALL_USERS=true`** → anyone can message (use with caution)

### Group Access

Group access is controlled by the `SIGNAL_GROUP_ALLOWED_USERS` env var:

| Configuration | Behavior |
|---------------|----------|
| Not set (default) | All group messages are ignored. The bot only responds to DMs. |
| Set with group IDs | Only listed groups are monitored (e.g., `groupId1,groupId2`). |
| Set to `*` | The bot responds in any group it's a member of. |

---

## Features

### Attachments

The adapter supports sending and receiving:

- **Images** — PNG, JPEG, GIF, WebP (auto-detected via magic bytes)
- **Audio** — MP3, OGG, WAV, M4A (voice messages transcribed if Whisper is configured)
- **Documents** — PDF, ZIP, and other file types

Attachment size limit: **100 MB**.

### Typing Indicators

The bot sends typing indicators while processing messages, refreshing every 8 seconds.

### Phone Number Redaction

All phone numbers are automatically redacted in logs:
- `+15551234567` → `+155****4567`
- This applies to both Hermes gateway logs and the global redaction system

### Note to Self (Single-Number Setup)

If you run signal-cli as a **linked secondary device** on your own phone number (rather than a separate bot number), you can interact with Hermes through Signal's "Note to Self" feature.

Just send a message to yourself from your phone — signal-cli picks it up and Hermes responds in the same conversation.

**How it works:**
- "Note to Self" messages arrive as `syncMessage.sentMessage` envelopes
- The adapter detects when these are addressed to the bot's own account and processes them as regular inbound messages
- Echo-back protection (sent-timestamp tracking) prevents infinite loops — the bot's own replies are filtered out automatically

**No extra configuration needed.** This works automatically as long as `SIGNAL_ACCOUNT` matches your phone number.

### Health Monitoring

The adapter monitors the SSE connection and automatically reconnects if:
- The connection drops (with exponential backoff: 2s → 60s)
- No activity is detected for 120 seconds (pings signal-cli to verify)

---

## Troubleshooting

| Problem | Solution |
|---------|----------|
| **"Cannot reach signal-cli"** during setup | Ensure signal-cli daemon is running: `signal-cli --account +YOUR_NUMBER daemon --http 127.0.0.1:8080` |
| **Messages not received** | Check that `SIGNAL_ALLOWED_USERS` includes the sender's number in E.164 format (with `+` prefix) |
| **"signal-cli not found on PATH"** | Install signal-cli and ensure it's in your PATH, or use Docker |
| **Connection keeps dropping** | Check signal-cli logs for errors. Ensure Java 17+ is installed. |
| **Group messages ignored** | Configure `SIGNAL_GROUP_ALLOWED_USERS` with specific group IDs, or `*` to allow all groups. |
| **Bot responds to no one** | Configure `SIGNAL_ALLOWED_USERS`, use DM pairing, or explicitly allow all users through gateway policy if you want broader access. |
| **Duplicate messages** | Ensure only one signal-cli instance is listening on your phone number |

---

## Security

:::warning
**Always configure access controls.** The bot has terminal access by default. Without `SIGNAL_ALLOWED_USERS` or DM pairing, the gateway denies all incoming messages as a safety measure.
:::

- Phone numbers are redacted in all log output
- Use DM pairing or explicit allowlists for safe onboarding of new users
- Keep groups disabled unless you specifically need group support, or allowlist only the groups you trust
- Signal's end-to-end encryption protects message content in transit
- The signal-cli session data in `~/.local/share/signal-cli/` contains account credentials — protect it like a password

---

## Environment Variables Reference

| Variable | Required | Default | Description |
|----------|----------|---------|-------------|
| `SIGNAL_HTTP_URL` | Yes | — | signal-cli HTTP endpoint |
| `SIGNAL_ACCOUNT` | Yes | — | Bot phone number (E.164) |
| `SIGNAL_ALLOWED_USERS` | No | — | Comma-separated phone numbers/UUIDs |
| `SIGNAL_GROUP_ALLOWED_USERS` | No | — | Group IDs to monitor, or `*` for all (omit to disable groups) |
| `SIGNAL_ALLOW_ALL_USERS` | No | `false` | Allow any user to interact (skip allowlist) |
| `SIGNAL_HOME_CHANNEL` | No | — | Default delivery target for cron jobs |