A good friend of mine has a pair of guard dogs that bark as soon as you take a step toward her house.
They bark even louder when you ring the doorbell. And when the doors open and she lets you in, they bark even more. Sometimes, they toss in a couple of growls for good measure. But eventually, these two protectors of the house -- combined, they weigh about four pounds -- tire out, go to their respective corners and curl up for a snooze.