"Roland Perry" wrote in message
...
In message , at 05:31:00 on Tue, 17 Mar
2015, john james remarked:
There is. You take the "pattern" from a TV programme currently being
broadcast, and subtract it from the total. You ten see if what remains
matches any of the other TV programmes currently being broadcast.

If it doesn't batch, then try a second TV programmes... iterate until
you find two whose patterns do add up to the total.

Its a bit more difficult than that..

different TVs take different times to decode the signal to put on the
display.

That's trivially taken account of when matching up the patterns.

No it isn't, particularly when you only have 4 second samples of the
total house current.

We aren't looking for picture brightness altering second by second. More
from one shot to another.

Trouble is that when you don't know when the shots change,
you have to sample the total house consumption at a decent
rate to be able to work out the backlight level for each shot.

And smart meters used by electricity supply authorities
do not sample at anything like a 4 second rate anyway.
They in fact actually integrate the total current consumption.

different TVs have different response times for the backlight.

That will only affect the amplitude of the peaks/troughs, not their
size.

But it does mean that you can't just add every pair of channels broadcast
and see which matches the pattern you see on the house current.

You can try every pair until you get one which matches close enough.

No you can not when the two TVs are not identical designs.
If you can't assume identical TV designs, you don't even know
how to add to the two channel candidates together to get the
total of the two backlight currents to compare with the total
house current.

In practice you are actually eliminating the ones which don't match at all
(for example two channels where the picture is simultaneously dark, but
the current consumption indicate that at least one is bright).

But you can't even do that when the smart meter integrates
the total house current and only reports every 15 mins or so.

And there are those who check the other channels during ad breaks too.

See below - although add breaks in the UK are only 4 minutes, four times
an hour, and there's plenty of programme material in between to use as a
comparator.

Cut the ad breaks are not synchronised, so you can't even work out
when a particular channel is in an ad break even if you did have the
total house current every 4 seconds, and you don't have anything
like that.

In fact you'd only be trying to do the comparison during the
programme segments because different regions of the country have different
advertisements.

But there is no way to work out when it is an ad break.

It's claimed to be a 100% solution.

Presumably you meant "It isn't"

Yes.

So in practice its going to be quite hard to tell what TV programs you
are watching even if the smart meter could collect the data and send it
somewhere to be analysed which is going to be difficult as they use SMS
messaging and not the internet and the GSM control channel would be
swamped very quickly if a few meters started sending SMS every second.

The data can be batched up and sent later, but how long will smart
meters be using 20th Century comms when they are sat in the same under
the stairs cupboard as the ADSL router?

The point is that is how they work, so can't be used to snoop on what
you are watching when you have more than one TV used at once or
even just one when you are doing that with every smart meter.

It's not for snooping on everyone at once.

Its even less likely that say MI5 will be snooping on a particular
house to see who is watching the latest footage about ISIS avidly.

And the smart meters don't provide anything like enough data to
do that anyway.

In fact it's not really about snooping on anyone's TV schedule.

There is no other reason to try to work out what is being watched
on the TVs in the house.

I think you've lost sight of the original proposition that "IF (as you
can) you can tell what TV programme someone is watching,

No evidence that you can do that even with one TV given what
data the smart meter does provide to someone outside the house.

you can also
tell whether they've got other appliances like deep freezes,

You can do that even if you can't work out what is being watched
on the TV.

and hence
how much such appliances are taking; and you can tell what time someone
gets up in the morning etc).

You can do that trivially my just watching when the total house current
increases in the morning as they get up, turn the light(s) on and do other
stuff like have a ****, and put the jug on to have something to drink etc.

Even with someone like me that doesn't drink anything hot at all first
thing in the morning, its easy enough to see when I cook the toast.

Think of it like saying "if I can slip a bit of 200gsm card through this
gap in the window frame then there's going to be a draught when the wind's
blowing", and then everyone pitching in with objections like:

Only if the wind's blowing from that direction
Not if the gap still has the bit of card in it
I only have 100gm card and putting two of them in the gap isn't the same
Who wants to put a bit of card in *everyone's* window anyway

I've never been into analogies, they don't help with the question
of whether its actually possible to work out what someone is watching
on two TVs given the data that can be obtained from a smart meter.