Simplify the following text for a Grade 5 native English-speaking person.
Original: Some breeds ( such as Keeshonden ) are excellent watchdogs but not excellent guard dogs because they bark loudly to alert their masters of intruders but are not given to assertive behavior . Similarly , even very small but attentive dogs ( among a few other species ) may function well as watchdogs .
Simplified: Such dogs are called watchdogs and do not usually become a guard dog .