When I was in my teens, I picked up the idea of  "triple redundancy" as the NASA standard for fail-safe systems. The idea being, your backup also has a backup, so a catastrophic failure would require 3 (hopefully) independent things to fail at the same time. Without litigating whether this was actually a NASA design principle, or whether a more apt description is "triple failure, double redundancy, I can say the concept of redundancy made an impression on my youthful self.

Think about losing or misplacing your car keys. If you lose track of your primary key one day a month (1/30), adding a backup key takes that to once in 3 years (1/30^2). Add another backup, and you are at something like once over an entire lifetime (1/30^3 = 1/27000). And that is ignoring the fact that, once down to your second backup, you are probably going to be really, really careful.

Anyway, this week I experienced a rare quadruple redundancy failure--this time related to housekeys, not car keys.

We are having our siding replaced, so the garage keypad was removed (and resting inside the garage, where the workers left it). I idly noted that, as I walked out the garage, and walked to my car. What was I getting in the car to do? I was going to drop it off for service, and bike home. So that took out another source of access, when I returned home (via bicycle--that is how I minimize the pain of vehicle drop-offs)--no garage door remote. 

But I have never been one to rely on the garage for access, since if the power goes out (relatively more likely), or the opening system has a problem (even less likely), you are SOL. I keep a housekey on our keychains. BUT, we have a new car, and I haven't installed the housekey yet.

Still, I wasn't worried, because I also have a Tailwind smart garage door opener. I can easily open the garage door from my phone. Except it was this night my Tailwind chose to fail me (I think because of a required update). So had my wife not been at home, I would have experienced 4 system failures, resulting in lockout.

(I have since placed the keypad on the back deck, as a temporary backup, until the siding work is done.)