No, your contacts won't automatically know you're using a 2ndLine number. Here's why:

  • Caller ID: When you call someone with your 2ndLine number, they'll only see your chosen 2ndLine number displayed on their phone, not your personal number. This keeps your information private and allows you to manage different communication channels separately.

  • No notifications: 2ndLine doesn't send any automated messages to your contacts informing them you're using the app. So unless you explicitly share your 2ndLine number with them, they won't know your calls or texts originate from there.

  • Customization options: For increased privacy, you can even: 
    • Choose a different display name for your 2ndLine number when making calls.
    • Set custom ringtones for different contacts using your 2ndLine.
    • Utilize anonymous calling feature (if available in your plan) to completely mask your number.

Remember, even though your contacts won't automatically know you're using 2ndLine, it's always good practice to be transparent about your communication methods if necessary, especially for personal or professional scenarios.

Additional points to consider:

  • Some countries or regions might have regulations regarding caller ID and anonymity. Always comply with local laws when using 2ndLine.
  • Be mindful of potential spam filters as some recipients might have stricter settings that could flag unknown numbers.