What is a trusted device?
You can designate a PC or other device (like a Windows Phone, a Surface, or another tablet), as a trusted device to use with your Microsoft account. When you use a trusted device to perform sensitive actions like resetting your password or managing your billing info, you can automatically verify your identity without having to enter a security code each time.
To add a trusted device to your Microsoft account
Sign in to your Microsoft account.
Under Password and security info, tap or click Edit security info.
Because you're changing sensitive info, you'll be prompted to enter a security code.
Check your alternate email or your phone for a code sent by the Microsoft account team, and enter it in the text box.
Select the I sign in frequently on this device. Don't ask me for a code. check box, and then tap or click Submit.
You can now edit your info on this device whenever you want, without entering another security code.