name: vmi-reverse-engineering description: This skill should be used when the user asks to "reverse engineer VMI", "capture BLE traffic", "analyze VMI protocol", "control VMI app via ADB", "pull btsnoop logs", or discusses Ventilairsec device protocol analysis.

VMI App Reverse Engineering

Control the Ventilairsec VMI+ app via ADB to capture and analyze BLE protocol traffic.

Quick Start

# 1. Enable BT snoop logging (one-time setup)
./scripts/capture/vmictl.py btsnoop-enable
 
# 2. Connect to device
./scripts/capture/vmictl.py connect
 
# 3. Start capture session
SESSION=$(./scripts/capture/vmictl.py session-start my_session)
# Navigate, take checkpoints, record values, then end session
./scripts/capture/vmictl.py session-end "$SESSION"

For phone setup, ADB connection, BT snoop logging details, and troubleshooting, see playbook.md section 1.

App Control Commands

Connection

Navigation (from home screen)

Maintenance Screens

Configuration Screens

Schedule Controls (from Time Slot Configuration)

Sensor Selection (from Sensor management)

Fan Control (from home screen) ⚡

Holiday Mode (from Special modes screen) ⚡

⚡ = modifies VMI state. These commands (plus airflow, airflow-min, airflow-max, preheat-temp, summer-limit, firmware-update) are automatically logged to data/captures/vmi_actions.log. If a capture session is active, an automatic checkpoint (screenshot + timestamp) is also taken — no need to call session-checkpoint manually.

Utility

Bluetooth Capture

Screen Hierarchy

HOME (fan control buttons)
├── menu
│   ├── Configuration
│   │   ├── Simplified (airflow slider)
│   │   ├── Special modes (holiday, night vent, fixed airflow)
│   │   └── Time slot configuration
│   ├── Maintenance
│   │   └── Available info
│   │       ├── Equipment life (filter days, serial)
│   │       ├── Instantaneous measurements (temp/humidity)
│   │       └── Diagnostic (component health)
│   └── Sensor management (probe selection)

Capture Session Workflow

# 1. Start session (outputs directory path)
SESSION=$(./scripts/capture/vmictl.py session-start humidity_test)
 
# 2. Navigate to screen, take checkpoint (outputs screenshot path)
SCREENSHOT=$(./scripts/capture/vmictl.py session-checkpoint "$SESSION")
 
# 3. Read the screenshot to see values, then append to checkpoints.txt
 
# 4. State-modifying commands auto-checkpoint when a session is active:
./scripts/capture/vmictl.py fan-max  # auto-checkpoint with note "action=fan-max"
 
# 5. End session and pull btsnoop logs
./scripts/capture/vmictl.py session-end "$SESSION"

After each checkpoint, append observed values to $SESSION/checkpoints.txt:

remote_temp=19
remote_humidity=55
probe1_temp=16
probe1_humidity=71
notes=after switching to Probe1 sensor

Note: State-modifying commands (fan-*, boost, preheat-toggle, preheat-temp, airflow*, holiday-*, firmware-update) automatically create a checkpoint when a session is active. You only need manual session-checkpoint calls for read-only observations (navigating to a screen to record displayed values).

Packet Analysis

# Basic extraction
python scripts/capture/extract_packets.py session/btsnoop.log
 
# With checkpoint correlation
python scripts/capture/extract_packets.py session/btsnoop.log \
    --checkpoints session/checkpoints.txt --window 10
 
# Export status packets as hex
python scripts/capture/extract_packets.py session/btsnoop.log --status-hex

For packet type reference, field offsets, and encoding details, see protocol.md.

Instructions for Claude

When helping with reverse engineering:

1. Before capturing: Ensure BT snoop is enabled with btsnoop-enable
2. For new protocol fields: Use capture session with checkpoints
3. Record values: Read each checkpoint screenshot, append values to checkpoints.txt
4. Compare packets: Use --checkpoints flag to correlate bytes with app values
5. Navigation: Follow screen hierarchy - can't jump directly to submenus
6. Verify results: Check screenshots in session directory

Phone Battery Monitoring

The Fairphone used for reverse engineering is not plugged in and will eventually run out of battery. The vmictl script automatically checks battery level every 5 minutes and prints a warning to stderr when it's low.

You MUST relay battery warnings to the user. When you see output containing BATTERY WARNING or BATTERY CRITICAL from any vmictl command:

• WARNING (<= 20%): Immediately tell the user: "The phone battery is at X% — it should be charged soon to avoid losing the session."
• CRITICAL (<= 10%): Stop what you are doing and alert the user: "The phone battery is critically low (X%). It needs to be charged NOW or it will shut off and we'll lose BLE connectivity."

You can also check manually at any time with ./scripts/capture/vmictl.py battery.

Opportunistic Data Collection

At the start of any VMI debugging session, run the sensor collection command:

./scripts/capture/vmictl.py collect-sensors

This command:

1. Checks if 15+ minutes have passed since last collection (skip if too recent)
2. Navigates to Instantaneous Measurements screen
3. Takes a screenshot and pulls btsnoop logs
4. Extracts packet byte values and displays them for comparison

Use --force to collect even if less than 15 minutes have passed.

After running, read the screenshot and compare app values to packet bytes. If values differ, add a timestamped note in the current investigation issue/logbook.

Data is stored persistently in data/captures/ (gitignored, survives reboots).