An email when a new device signs in

When a device you aren’t already signed in on signs in to your account, the server sends you a New sign-in email. It names the device and its platform and gives the time in UTC. There’s no location in it: the server doesn’t look up where IP addresses are.

If it wasn’t you, sign that device out in Settings → Devices and change your master password: whoever it was knew your master password and Secret Key.

You won’t get one when a device you’re already signed in on signs in again, for the first sign-in right after you create your account, or when a recovery code was used (that sends its own email). See authentication.