Apple Watch — TAK Can

Architecture

The Watch never opens a direct TAK server connection. All network operations flow through the paired iPhone via Apple's WCSession framework. This preserves Watch battery and simplifies security — the Watch is a sensor and quick-input terminal.

┌──────────────┐   WCSession    ┌──────────────┐   TLS/Mesh   ┌────────────┐
│  Apple Watch │◄──────────────►│    iPhone     │◄────────────►│ TAK Server │
│              │                │              │              │   / Mesh   │
│ • Vitals     │  sendMessage   │ • Broadcasts │              └────────────┘
│ • Chat       │  transferUser  │   vitals in  │
│ • Emergency  │  Info (queued) │   CoT SA     │
│ • Compass    │                │ • Relays chat│
│ • Dead Man   │                │ • Sends      │
│ • Status     │                │   emergency  │
└──────────────┘                └──────────────┘

Features

❤️ Health & Vitals

Passive monitoring — no workout session required, minimal battery impact. Readings are event-driven (HealthKit background delivery) and sent to the phone on each new sample.

Vital	Source	Frequency
Heart Rate	HKAnchoredObjectQuery + background delivery	Every few minutes (Watch decides)
SpO2 (Blood Oxygen)	HKObserverQuery	Periodic (Watch decides)
Steps	HKStatisticsQuery (cumulative today)	On each SpO2/HR update
Active Calories	HKStatisticsQuery (cumulative today)	On each SpO2/HR update

The phone injects vitals into the CoT SA broadcast as a <health> XML extension. Other TAK clients see your team's vitals in real time.

<health>
  <vitals heart_rate="72" spo2="98" steps="4521"
          active_calories="312" source="Apple Watch"
          timestamp="2026-04-06T15:30:00Z"/>
</health>

Per-vital sharing controls on the phone let you choose exactly which vitals are broadcast.

💬 Chat

Read and reply to messages directly from your wrist. The Watch receives the latest messages from the phone and displays them in a scrollable list. Reply via dictation, scribble, or suggested responses.

Unread message count badge on the main menu
Group channels and direct messages
Messages sent via WCSession to phone, which broadcasts to server/mesh

🚨 Emergency Beacon

Trigger an emergency alert from your wrist that broadcasts to all connected TAK servers and mesh peers. Designed for reliability:

Guaranteed delivery — uses transferUserInfo which queues the message and delivers when the phone is reachable, even if temporarily disconnected
Rate limited — 5-second minimum interval prevents accidental double-tap
Cancel from Watch or phone
Visual indicator when emergency is active

Watch → Phone (transferUserInfo, guaranteed):
{
  "action": "initiateEmergency",
  "emergencyType": "911"
}

Phone broadcasts CoT:
<event uid="..." type="b-a-o-tbl" ...>
  <detail>
    <emergency type="911 Alert" cancel="false"/>
  </detail>
</event>

🧭 Compass

Real-time heading display using the Watch's magnetometer. Shows cardinal direction and numeric bearing. Useful for quick field orientation without pulling out your phone.

True heading (magnetic declination corrected)
Cardinal direction indicator (N, NE, E, SE, S, SW, W, NW)
Rotating compass rose

🏴 Quick Status

Send predefined status codes to your team with a single tap. Status is broadcast as a CoT message visible to all connected clients.

💀 Dead Man's Switch

Automatic safety check — if the Watch detects no movement or interaction for a configurable period, it triggers an automatic emergency alert. Designed for solo operators in hazardous environments.

Configurable timeout period
Warning prompt before triggering — tap to dismiss and reset timer
If no response → automatic emergency broadcast via phone
Visual indicator when enabled

Timeline:
  [Activity detected] → Timer resets
  [No activity for N minutes] → Warning vibration + screen prompt
  [No response for 30 seconds] → Auto-trigger emergency
  [User taps "I'm OK"] → Timer resets, no alert sent

Watch App Screens

Screen	Purpose	Key Info
Main Menu	Navigation hub	Connection status, unread badge, emergency indicator
Chat	Read/reply messages	Latest messages, dictation input
Emergency	Trigger/cancel alert	Emergency type selection, active status
Status	Quick status codes	One-tap status broadcast
Compass	Heading display	Bearing, cardinal direction, compass rose
Health	Vitals monitoring	HR, SpO2, steps, calories, last reading time
Dead Man	Safety timer	Enable/disable, timeout config, status

Battery Considerations

No workout session — passive HealthKit queries only, no continuous sensor drain
Event-driven updates — Watch sends to phone only when new data arrives, no polling timer
No direct network connections — all comms via WCSession (low power)
Background delivery — HealthKit wakes the app briefly for new readings, then suspends

Supported Devices

Apple Watch Series 5 and newer running watchOS 10.0 or later. Requires a paired iPhone running TAK Can.

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