The recommended sign-in/verification methods for multi-factor authentication are the Authenticator App and your mobile phone number, but if you do not have a mobile phone there are other options:
You can register your home phone number, but that will work only when you are home. You will not be able to sign-in when you are in other off-campus locations.
You may purchase a hardware security key for MFA.
Types of hardware security keys
The type of security key you should purchase is a FIDO2 key, but you need to make sure you purchase one that will work with your off-campus device(s).
Most FIDO2 keys cost between $20 and $50. Popular brands include Yubico (maker of the Yubikey), Token2, and Thetis.
Keys vary by material, ruggedness, water-resistance, and interface. The most important consideration is the interface:
Buy a security key that has a USB-A interface if you plan to use it with a desktop computer at home (Mac or PC)
Buy a security key with a USB-C interface if you have a Macbook or PC laptop that has only a USB-C port.
Optional features include NFC for wireless sign-ins on an Android device, but if you have a device capable of running Android or iOS we recommend just using the Authenticator app.
Adding your security key as an MFA sign-in verification method
Go to https://mysignins.microsoft.com/security-info to add a new sign-in verification method.
Click the Add Method button.
Choose Security Key and click the Add button.
Follow the on-screen instructions to finish setting up your security key.