(#11) S.P.O.F. 

Here’s a real life example of how a Home Automation system failure can really stink. Let’s say your carefully crafted Home Automation system is humming away as you leave the house on an extended vacation.  And let’s say you’re heading into the remote wilderness of Southern Utah.

Well, the destination is immaterial, but let’s say you’re heading far, far away from home. 

Oh yes – you've got wireless connectivity. Our example doesn't work if you can’t connect to the ‘net.

For the first four days of your vacation, you check your Home Automation Status page and see that your system is working well.  The doors are all reporting closed, the water leak sensors say they’re dry and the motion sensors see nothing.

Now – the fun part. On day five, at 9:32 pm, your system tells you that the big garage door has just opened. Whoa!  You’re not home, you’re sure of that! And you’re pretty sure no one else has good reason to open the door.

Quick – check the Home Automation Status page.  Yes – the garage door is reporting that it’s Open. It’s saying the Battery is OK and that the sensor is reporting its On-line and functioning.  Check the other sensors: have they entered into the house?  No – the door sensors are closed and have been closed. The motion sensor says No Motion.  Are they rummaging around in the garage?  Maybe the rat-bastards are after my TwentyYearOld, WillNotDie John Deere Weed Whacker!  Or maybe they’re going for the Pizza Hot Pocket snacks in the freezer out there.

Recheck the other sensors – the doors are still showing closed and there’s still no motion.

False Alarm?

But why now?  

The garage door sensor has been working well for weeks.  

Why now?  

Why, at 9:32 pm when I’m 1400 miles from home?

Reliable, Dependable and Trustworthy!

So let’s switch gears and talk about reliability.

Reliability engineering is something I know nothing about. So, like movie critics, I’m allowed to pontificate and make wild assumptions.  I know it’s hard.  Reliability engineering, that is. It’s got to be hard – or Three Mile Island wouldn't have had a problem; Chernobyl wouldn't have blown up; the Therac-25 wouldn't have killed people.

• How do you make a system reliable?  
• How do you make it reliable and still affordable?  

Add a second sensor? No – there’s that old proverb: “Man with two watches never knows what time it is.” Add a third sensor?  I've read that’s what they do in Avionics, reliability through redundancy.

Wait – reliability is not at the heart of this system. It’s something else. It’s trust.

In this case, what we've lost is trust. I can’t trust my system anymore.  

Oh -- it works, mostly. 

It works usually. 

And you know what?  

That was the same problem we had with X10 technology.  It worked, usually.

Avionic systems also have enough sensors it’s possible to make deductions on whether a sensor has failed. If one sensor reports something that might claim the plane is flying upside down, yet all of the other sensors indicate normal flight, odds are that we have a sensor failure.

In my house, I can make some deductions.  If an interior door suddenly opens, yet the nearby motion sensor indicates stillness and the exterior doors have remained closed – then odds are it’s a false alarm.  

But not with the garage door sensor.  It’s perfectly reasonable for the door to open at 9:32pm.  Just not when we’re all on vacation.

• Trust.
• Trust is earned.
• Trust is earned over time.  

Once lost, it’ll take a while to earn it back.  We’ll be home from vacation in about two days.  I’ll debug the garage door sensor.  Hopefully the failure will be obvious. Maybe the sensor fell off the door.

Two Days Later -- Epilog

That was it – mechanical failure. The Velcro that held the sensor to the door gave way, the sensor fell off the door and landed in a tilted (open) state.  One #4 wood screw and we’re back in business.

For want of a nail, err, screw...
To borrow the Wisconsin State Motto: foreward!