Zooz just announced a plug-in Z-Wave network extender, based on the new 800 series platform (an overview of Z-Wave Long Range). This battery-backed plug-in module is only an inch in diameter, and can also be used to monitored the status of your power source.
Some technical articles can be found on the Zooz website, or if you're interested in a more detailed description, check out The Smartest House's website, which has the device on sale at an introductory price (but ships with beta firmware).
Just an FYI, as we have a lot of HomeSeer users here...this device will only act as a repeater and not report power outages. Not a big IMO and worth it if it works as promised. Looking forward to anyone getting this device to report back here on its performance.