I was thinking would it be cool if customers can turn on "valid devices" so they can sign in to their account.

After logging in on a unknown device they get a code sent to their client email address where they have to enter it and add the device to their "verified" lists.

Clients should be able to remove the devices from the client area if they wish.

Valid Devices:
[iPhone 7] [Mac Address] [IP Address] [Last logged in date] [x]
[Macbook Pro] [Mac Address] [IP Address] [Last logged in date] [x]
[Windows 10] [Mac Address] [IP Address] [Last logged in date] [x]