This energy monitoring transmitter, known as emonTx, is an Atmega328-based small wireless energy monitoring node. It also fully compatible with Arduino IDE. EmonTx is designed to take inputs from multiple CT sensors, optically from a pulse-output utility meter and from multiple one-wire temperature sensors.
The design is based on the JeeNodeV5 by Jean-Claude Wippler and uses 2x AA batteries or 5V USB as power source.
For more detail: Energy Monitoring Transmitter using Atmega328 microcontroller