As a security measure, you will receive an email about an unrecognized device each time you access your account after a period of inactivity from a different IP address, device, or web browser.
What is an unrecognized device?
An "unrecognized device" just means something is different about how you accessed your account from the last time. It does not necessarily mean someone other than you is attempting to access your account.
Many reasons 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 use the same browser to access your account, the new version causes it to be "unrecognized." Alternatively, you could use a different device to access your account, 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 use the same device as last time to access my account?
You may disregard the email if you receive an unrecognized device email after using the same device as last time to access your account. You likely received the email because your IP address differed from the last time you accessed your account using the same device.
If you know you accessed your account, you can ignore the unrecognized device email.