In order to use Day One Sync, an account is required. You can create an account with an email and password, or you can use Apple ID to sign in. Be sure to sign in with the same credentials on all devices in order to sync your data.
Here is how to set up an account.
Web
Go to https://dayone.me and click Create account.

iOS
Open Day One > Settings > Sign In > New User
Enter your email address or choose Sign up with Apple ID
If you entered your email, follow the instructions in the email
If you chose Apple ID, you are signed in using the credentials stored in your device Settings. This is secure. See here how we use Apple ID to sign in.

macOS
Open Day One > Settings > Sync
Click Sign In
Click Create Account at the bottom or choose to sign in with Apple ID.


Android
On Day One Android, you can sign in using your Google account or create a new Day One account. We recommend signing in with your Google account.
Open Day One > Settings > Sign In > New User
Select the Google account you would like to use or tap “Use another account” to sign into a different Google account.
Your account will automatically be created.
If you want to sign into your other devices, go to app.dayone.me/settings > Sign in with your Google account > Click Add Password. You can then sign into Day One on your devices using your Google email address and password.

Manage your sync account
Sign in to the web app and click “All Entries” to view your synced entry count and also to manage your Day One Sync account.