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I've recently seen some commotion online about "smart meters," electronic power consumption meters that are replacing the mechanical meters in some areas. My understanding is that these meters have radio transmitters that broadcast each household's power consumption (I'm not sure where these transmissions are received) once or several times per day (the effectiveness of this is discussed in this question).

One example of such commotion is this YouTube video, which claims that smart meters are an invasion of privacy, because:

  • They can see when you turn appliances on and off. This seems to imply that smart meters transmit real-time data. I would think that they would transmit a running total at intervals, rather than the power consumption on a per-minute or per-hour basis.
  • They can measure the power consumption of individual appliances. I'm extremely skeptical of this. Electricity just doesn't work that way. If the point above is true, then at best they could guess at what kind of appliance is on just after it was turned on, based on the increase of consumption. But that wouldn't be accurate at all.
  • They record your personal living patterns. This follows from the other two, and is the ultimate conclusion that smart meters will be used as surveillance devices.

Is the breadth of information visible to a smart meter anywhere near this level of accuracy? It defies my understanding of how electricity works in a home, but that understanding is far from complete. From what I've seen, the people spreading this warning are unusually calm and well spoken, and it's causing me to second guess myself.

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    "Sure, grow-ops are illegal, and if you're not doing illegal things, you've got nothing to worry about." -- Pretty much any violation of rights and draconian action can be justified this way. Whether or not they are a violation of rights, this is the worst defense of a law. By that reasoning we should put jaywalkers to death. After all, if you're not doing anything illegal you have nothing to work about.
    – Russell Steen
    Jul 29, 2011 at 5:54
  • @Russell I completely agree, but I don't know if claiming a violation of rights is valid here -- it feels to me like saying ISPs are evil because the logs they keep can incriminate you. I think the smart meter data has the side effect of being supporting evidence if it's subpoenaed, much like any other information about you kept by various companies and agencies, so calling it draconian is a bit of an overreaction.
    – Carson Myers
    Jul 29, 2011 at 6:14
  • Hi Carson, can you please limit this question to one verifiable fact please? As it is it will tend to generate a bunch of speculation...
    – Sklivvz
    Jul 29, 2011 at 6:18
  • @Sklivvz updated to include only three points, which are related to each other.
    – Carson Myers
    Jul 29, 2011 at 6:26
  • Interesting extra privacy issue: the security implications if someone were to hack into these (I have seen this demonstrated) they could see when you were out, on holiday etc...
    – Rory Alsop
    Feb 27, 2012 at 23:12

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The IEEE Spectrum magazine has discussed this issue in the past. Apparently it is clear from the data generated by these meters that certain appliances can be easily distinguished from others with reasonable accuracy and certainty. They reference a study from the NIST which illustrates

frequent meter readings may provide a detailed timeline of activities occurring inside a metered location and could lead to knowledge about specific equipment usage

And they use this graph to demonstrate: NISTIR 7628 Volume 2 Figure 5-1: Power Usage to Personal Activity Mapping

So basically because they sample the total energy flow at a fairly high frequency, they can estimate which devices are being used at which times based on the characteristics of those devices, which for a utility company should be easy to determine. It isn't perfect, but it's accurate enough especially if it can be correlated with smart meters for water, etc, because then they can map water usage to dishwashers, etc, and more accurately determine which electrical loads correspond to which major appliances.

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  • That's interesting, I didn't realize the peaks had such definite shapes.
    – Carson Myers
    Jul 29, 2011 at 21:57
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    I don't see how they can apart toaster and kettle.
    – vartec
    Jul 31, 2011 at 9:34
  • @vartec: The toaster has an immediate drop-to-zero when finishing, the kettle maintains a slightly larger consumption for a few minutes after finishing - probably because electric kettles have lights that remain on even while not actively heating.
    – user792
    Jul 31, 2011 at 10:22
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    @Joe: I don't buy it. Only some models have any lights at all, and ones that do, have LEDs, which are have power consumption so low, that it wouldn't be noticeable on this graph.
    – vartec
    Jul 31, 2011 at 16:54
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    @Aaronaught: That may be true now (I'm not sure and a quick scan of the NIST report didn't reveal what hardware they used nor its installed base size) but I think it's a safe assumption that as utilities find a use for higher-frequency sampling they'll deploy the meters for it.
    – Mr. Shiny and New 安宇
    Aug 5, 2011 at 14:54

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