Thanks for reaching out here in the Community. I'm sorry to hear if all of your Nest Protects are showing offline. To know more about this, I'd like to ask if there were any recent changes made to your Wi-Fi network? Were there any recent power outages? (In case you have a wired Nest Protects). What troubleshooting steps have you done so far?
Give these steps a try:
Try performing a safety check.
With the Nest app on your mobile device: If you have at least one 2nd gen Nest Protect in your home, you can run a Safety Checkup with the Nest app.
Try updating the Wi-fi information in the Nest app.
Looking forward to your response.