The purpose of the watchdog - the real one - is to deter thieves from your house. Of course, you will lock the door as the first measure, and will build a fence in areas where it's appropriate/usual. You can also employ some electronics. Or, you can simply leave your house open (or at least unlocked) if there is a small occurrence of thieves around, and there is a permanent watch on the neighbourhood or something similar. Or, you can simply live in a cottage with apparently nothing worth to be stolen. There are many people chosing NOT to have a watchdog, and perhaps even more who DO have a DOG, but not explicitly for the purpose of WATCHING; others do have a dog BECAUSE of watching, but they have no assurance that the dog WILL watch. Anyway, perhaps nobody would rely on the dog as the SOLE measure against thieves.

But the reason why the watchdog might work, even if not perfected for the task, is, that 1. it is in a combination of the "conventional" measures; 2. it is DIFFERENT than the conventional measures. It is not just an another door, another camera.

This is why the watchdog in AT89C55WD fails. It is as if you would have the dog in the yard, and the house accessible from the street. If the thief is stupid and tries first climb over the fence to the yard to break through the window, it will be caught by the dog; but against the most common thief who just simply breaks through the door, the dog is useless.

And, if you mean the dog for watching, you will go for the breed intended for this purpose - the powerful and determined one, rather than a fancy, nice, handsome, sophisticated and well behaved one.

JW