I have seen this many times, and I strongly believe the idea does NOT relate to personal defense.
As was posted, should there be an emergency of any kind, the first responders would be shot.
Now, I wouldn't feel as strongly about this if it was during a JBT pot bust that was 'somehow mistakenly given the wrong address' type deal where the thugs bust down your door at 3AM...but the results would be the same and the penalties just as severe, if not worse.
You just can't leave a deadly weapon wired or strung to anything in your house. The chances of it nailing the right person are infinitesmal compared to the risk of harm to an innocent person!
If this guy had been HOLDING that gat, we never would have heard about it, as he would have been justified.
So, until SHTF for real, don't even go there!