One of the first and most important jobs for which dog breeds were created was that of the watchdog; humans have taken advantage of the dog's natural instincts to protect its territory and/or its family and directed them towards protecting the property or family of the dog owner (a dog will consider his human family his pack if trained properly). There are a number of breeds that have been traditionally viewed as watchdogs, such as German Shepherds or Rottweilers, though many dog owners are finding out that there are a variety of different dogs that make excellent watchdogs.
Watchdogs are different than "guard dogs"; the latter often means a dog that has been trained to attack or immobilize unwanted guests and foolish owners often encourage aggressiveness in dogs they intend to use as guard dogs. Watchdogs simply make noise when unwanted guests appear or when something seems out of the ordinary. Large dogs with deep barks can make good watchdogs, even if they're extremely friendly and trusting, as their size is often enough to deter intruders. But what about the Norwich terrier? Can such a small dog be a watchdog? Actually, some of the smallest dogs make the best watchdogs!
The Norwich terrier bonds very tightly to its family and will be wary of any new factor in its domestic equation; they are highly flexible and adaptable dogs, so it won't take them long to become familiar with a new friend or a new place, but anything they see for the first time will arouse their curiosity. And as terriers, they are very curious and alert dogs, being aware of and wanting to check out every sight and sound in the their surroundings. Given these characteristics, Norwich terriers will recognize a new face or something out of place in their environment and will be tuned in to it.
As terriers, they have a tendency to bark; without proper training, this barking can become annoyingly insistent, though with proper training it can become insistent only on the right occasions. Willingness to bark to alert owners is one of the main requirements of a good watchdog. Not only will the barking alert owners of a fishy situation, though, it also serves to alert intruders that they've been detected. And while intruders may be scared off by the deep bark of a large dog, the insistent ruckus that a small, yappy dog makes will be enough to convince them the whole neighborhood is looking out their windows.
Norwich are also incredibly intelligent animals and can often understand the difference between a new face that poses no danger and a dangerous intruder. Though their intelligence and determination can make it a task to train them, they are capable of learning a multitude of complex commands and can be trained to selectively bark in certain situations. Finally, though they're tiny, these dogs are fearless and, if properly trained, will not be intimidated easily, making them a great watchdog.