I don't know if I'd label this "smart grid." When they talk about
grid they mean long distance power station interconnections.
But this is a concern for individuals if they incorporate sufficient
memory into power meters. It is easy to tell if a house is occupied
by the types and times various loads come on and off - but it does
take some sophisticated algorithms to get much past large loads like
heaters, electric ranges, microwave ovens and water heaters. It is
possible to break out TV's, computers, compact fluorescent lamps,
etc., but not easy.
Power meters aren't exactly cheap, so unless there's a large campaign
to replace them it's probably not worth worrying about.
It may be possible for power companies to send out a read request
signal and alert police to a house's condition. Might be used in a
hostage situation for instance, or to determine if a suspect is in a
dwelling.
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I should think that the smarts would have to be very locally
installed. Therefore, my smarts box would end up with a .223 thru it.
If you live where you can't own a gun, then a baseball bat will do.