Zello Voice (PTT)

This skill covers the core push-to-talk voice feature — the heart of the Zello integration.

Core PTT Flow

1. Officer presses and holds the PTT button → Zello.send(contact)
2. SDK captures audio from microphone → streams to Zello servers in real time
3. Officer releases → Zello.stopSending()
4. Recipients hear audio as it streams (near-zero latency)

PTT is half-duplex — an officer cannot send and receive simultaneously.

PTT Hook

// src/features/zello/hooks/useZelloPTT.ts
import { useState, useCallback } from 'react';
import Zello, { ZelloContact } from '@zelloptt/react-native-zello-sdk';
import { requestZelloPermissions } from './useZelloPermissions';

export function useZelloPTT() {
  const [isSending, setIsSending] = useState(false);
  const [isReceiving, setIsReceiving] = useState(false);

  const startSending = useCallback(async (contact: ZelloContact) => {
    const granted = await requestZelloPermissions();
    if (!granted) return;
    Zello.send(contact);
    setIsSending(true);
  }, []);

  const stopSending = useCallback(() => {
    Zello.stopSending();
    setIsSending(false);
  }, []);

  return { isSending, isReceiving, startSending, stopSending };
}

PTT Button Component

Use onPressIn/onPressOut for press-and-hold behaviour. The app already uses expo-haptics — provide tactile feedback on transmit:

// src/features/zello/components/PTTButton.tsx
import { Pressable, Text, StyleSheet } from 'react-native';
import * as Haptics from 'expo-haptics';
import { ZelloContact } from '@zelloptt/react-native-zello-sdk';

interface PTTButtonProps {
  contact: ZelloContact;
  isSending: boolean;
  onPressIn: () => void;
  onPressOut: () => void;
}

export function PTTButton({ isSending, onPressIn, onPressOut }: PTTButtonProps) {
  return (
    <Pressable
      onPressIn={() => {
        Haptics.impactAsync(Haptics.ImpactFeedbackStyle.Medium);
        onPressIn();
      }}
      onPressOut={onPressOut}
      style={[styles.button, isSending && styles.active]}
    >
      <Text style={styles.label}>
        {isSending ? 'TRANSMITTING' : 'PUSH TO TALK'}
      </Text>
    </Pressable>
  );
}

Receiving Voice Messages

Register event listeners via Zello.Listener:

Zello.Listener.on('onIncomingVoiceMessage', (message) => {
  // message.contact — who is speaking
  // message.channel — which channel (if channel message)
  setIsReceiving(true);
});

Zello.Listener.on('onIncomingVoiceMessageStopped', () => {
  setIsReceiving(false);
});

History Playback

Replay missed transmissions:

Zello.playHistory(historyMessage);
Zello.stopPlayback(); // Cancel playback

Listen for playback events: onHistoryPlaybackStarted, onHistoryPlaybackStopped.

UX Guidelines

These patterns matter for officer safety and usability:

• Visual + haptic feedback during transmit — the button must feel responsive
• Receiving indicator showing the sender's identity (officer name/number)
• Disable PTT when isReceiving === true — half-duplex enforcement
• Transmission timer — display elapsed time for officer awareness
• Audio focus — the SDK manages audio focus, but avoid playing other sounds during PTT

Detailed Documentation

See docs/dev/zello/06-voice-messaging.md for the full voice implementation guide. For event details, load references/events-catalog.md.