Looking at my device timeline, I noticed that my subwoofer was no longer drawing power for the last few weeks. (It’s probably not something to easily hear while watching news, but for movies it makes a difference, of course.) Out of curiosity, I opened it up and noticed a few bulging capacitors. The subwoofer is from the era of the well known capacitor plague, Too bad. I guess I need to get a new one.
Suffice to say, without Sense it probably would have taken me a while longer to notice.
Great find @altenbach - sorry to hear about the Subwoofer!
This would also be a great story for https://sensesaves.sense.com/
Well, not really, because having a broken subwoofer actually saved electricity and replacing it will raise the consumption again. 
(… but wait, there’s more!)
Luckily, a local Costco still had a Klipsch R-12SW and I picked one up yesterday (Last day at $60off sale!). Sounds great so far, now I just need to find out why it does not go to standby when the receiver is off (The manual says that should happen after 15-20 minutes). Could my receiver still put out a spurious signal on LFE even if asleep? I guess I should hook it up to my solution for the old one.
Overall, the new subwoofer is significantly more power efficient while sounding great. The old one used 9W in standby and about 16W during use (see above link. Both fully calibrated with the setup mic of the receiver and at the same volume setting.) The new one uses only 5.5 - 6 W in typical use (I got it up to 10W by really cranking up the volume).
I am always amazed by the marketing. So the box of the new subwoofer says 400W amp. Apparently I am using way less than 2% of it! I don’t want to shatter my windows!!!
Maybe it’s one of those new LED subwoofers and it’s 400W equivalent.
He didn’t go for the CFL subwoofer? 
The Canadian Football League has subwoofers? Sorry, I am not good with acronyms…
OK, problem solved! While the Manual only mentions and explains two states for the switch (“On/Auto” and “off”), it is actually a three position switch with three states “On”, Auto", Off". Finally found the middle “auto” position and now it goes to standby when not in use. Standby power is true 0.00W!* (two decimal digits from Kasa!). Once the receiver goes on AND sound is playing, power goes up to ~5.5W again. Looks great!
*(earlier I said 1.5W, but that was only a very temporary state right after plugging it in, maybe while booting up)
From the Manual:
Back panel:
I corrected my statement above. the standby power is actually a true 0.00W. Even better!!!
(I also like the hidden Spinal Tap reference with the gain going all the way up to eleven 
)
OK, let’s revisit that idea! Maybe the old power trace was already a strong indicator of a failing subwoofer and all that random noise and high power-draw (even in standby!) was an early omen that I simply did not recognize at the time.
If we look at the numbers, maybe there was an extra 9W power leakage due to the amplifier already going bad fast.
If we remove that offset and noise, the two amplifiers are quite similar (~0W standby, ~6W use) and the 9W was additional and abnormal.
My knowledge of electronics is not sufficient to be sure about the exact mechanism, but the inner glass fuse of the old amp was actually blown, indicating that the current got high enough to take it out.
Interesting. I have an old Polk subwoofer that has a very similar control panel on the back. Even in “auto” mode the sub drew a good 10+W of power. Enough that it showed up very warm on a thermal imaging scan. I connected it to a plug strip that was controlled by the receiver power consumption, so now it only powers up when the receiver is on.
Is your 10W “standby” power relatively stable or as erratic as my old one? (Note that occasionally mine wildly fluctuated in the range of ~0…~13W, with the problem getting worse quite a few hours after going to standby.)
I don’t have any data right now, but IIRC it was relatively stable.
