Yorkshire Terriers were bred to hunt rats in Victorian mills and to tell their owners about it. Alerting you loudly to things is not a flaw in the breed, it's the job description. That doesn't mean you have to live with constant noise.
The important thing is that there's no single fix, because there's no single cause. Barking at the window is a different problem from barking when you pick up your keys, and the treatment that solves one makes the other worse. This guide helps you work out which type you're dealing with first.