As a security measure, each time you access your account after a period of inactivity, from a different IP address, device, or web browser; you will receive an email about an unrecognized device.
What is an unrecognized device?
An "unrecognized device" just means something is different about the way you accessed your account from the last time. It does not necessarily mean that someone other than you is attempting to access your account.
There are many reasons that may prompt this notice to you. One of the most common reasons is that an automatic update has been installed on your current browser. Even though you are using the same browser to access your account, the new version causes it to be 'unrecognized". Alternatively, you could be using a different device to access your account, or a different IP address or web browser. Sometimes, you may receive this notice because you are accessing your account after a period of inactivity.
What if I am using the same device as last time to access my account?
If you receive an unrecognized device email after using the same device as last time to access your account, you may disregard the email. You likely received the email because your IP address was different from the last time you accessed your account using the same device.
If you know it was you who accessed your account, you can ignore the unrecognized device email.