I did the Ac monitor with Arduino but I have a problem.
When nothing is pluged in, I have always a consummation (approximately 1,6 Watt)
What is the problem ?
A low power reading is usual when nothing is connected. This is due to noise in the CT and energy monitoring circuit. It's nothing to worry about, 1.6W is very low indeed. If needed you could add a line of code to set reading to be zero when reading is under 5W or so. The emonTx with the SCT-013-000 CT is designed to monitor up to 100A (24kW @ 240V), this setup is not optimal for monitoring low power levels. Greater precision at low power levels can be gained by using a larger burden resistor and a CT with less number of turns.
See this page for more information on CT sensors and calculating burden resistor values: http://openenergymonitor.org/emon/buildingblocks/ct-sensors-introduction
Open-source tools for energy monitoring and analysis. This project uses the GNU General Public Licence