this makes a lot of sense to me - many "mote" type sensors could have quite low duty cycles and very rare communication.
I always wonder about RF power harvesting, though: if I'm extracting power from a particular RF band, does that mean I'm hurting the propagation properties of anyone using that range of RF? does a harvester create a local RF hole, which might become more of a shadow for higher frequencies that need LOS?
It sounds like this technology "they can tell from the position of the handle whether the window is wide open, tilted open or closed" works on windows that crank open but not on common sash windows. Perhaps a version with magnetic contacts could detect the state of sliding windows. The biggest issue, however, is reliability. As the number of battery / energy harvesting sensor devices multiply in the house, homeowners become service engineers debugging and repairing failed sensors rather than the beneficiaries of the new technologies. When there are 100 sensors in the house, even a low failure rate becomes intolerable.