Google started beefing up Nest account security last year after a string of embarrassing but entirely preventable hacks. Part of that effort was mandatory two-factor authentication (2FA) for logins starting in spring 2020, and the time has come. Google says all Nest users will begin seeing 2FA prompts this month.
The latest 2FA changes only apply to those who have not migrated to a Google account or added SMS-based two-factor yet. If you're in one of those camps, you'll continue to log in as usual. Those still logging in with a Nest username and password only will get an email from [email protected] with a 6-digit PIN for each new login. Google hopes this will cut down on the number of account breaches because the account hijacker would need to have access to both your Nest and email accounts—hopefully they're not using the same password.
Google says it will notify everyone prior to flipping the switch on mandatory 2FA for their account. That should give you a chance to make sure you still have access to the email account associated with Nest. However, Google would probably still prefer that people migrate to a Google login for Nest for enhanced security.