Open-source hardware Arduino compatiable emonTx low power wireless energy monitoring node.
http://shop.openenergymonitor.com/emontx-v3/
http://openenergymonitor.org/emon/modules/emonTxV3
Hardware designs (schematics and CAD) files are licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License and follow the terms of the OSHW (Open-source hardware) Statement of Principles 1.0.