If you don’t want the hassle of a real dog (i.e. picking up poop, the cost, etc), but would like the protection, then ‘Secure Dog’ has you covered. The proximity alarm utilizes microwaves to see through walls, and when an intruder approaches within 20 feet the alarm emits a German Shepherd’s bark. The closer the intruder comes the more frequent the angry dog noise is sounded.
Available here for $81.