A watchdog is a dog that is highly alert and will raise the alarm by barking vigorously whenever someone approaches or enters your property. Watchdogs are different from guard dogs. (The job of guard dogs is to protect you and prevent intruders coming on your property in the first place, whereas the job of watchdogs is to raise an alarm.) The purpose of a watchdog is to alert you of danger. This is a list of the best watchdogs. These are dogs that are very alert and will always bark up a storm when a stranger approaches your home or enters without you knowing. All of these breeds in this list are excellent watchdogs.