I have 3 Nest Protect smoke / CO2 alarms 2 wired and 1 battery. I had to make changes to the naming of my WiFi network some months ago and since then I cannot get them back on the WiFi. Taking them down is not an option, life is too short… but connecting via app, I get blue ring on app and protect and nothing happens. Your software gives the user too little info.
Google Nest does not make it easy to change Wi-Fi settings in its devices, so they recommend, when changing Wi-Fi routers/modems, that you set the network name (SSID) and password to the same values used on the old router/modem.
If you can't do that, then Google Nest's process is to remove the Google Nest device from the Google Nest app or Google Home app (depending on the device) while you are still on the old Wi-Fi network, then do a factory reset, and then re-install while on the new Wi-Fi network.
I'm just another Google Nest customer; those are Google Nest's two options.
Some customers in this forum have reported varying degrees of success in contacting Support and getting walked through various ways to compel their device to factory reset even if they haven't followed the steps above.
@Johnhenryb thanks for posting here in the community. I understand your inconvenience when your Nest Protects can't connect to your Wifi network. Aside from updating the Wifi network from the Nest App, you may try these steps:
Looking forward to your response.
I appreciate your help, MplsCustomer.