thanks

With 400ma battery for one full year. I won't use a Arduino but something like some new very low power cpu! something like TI MP430 cpu. If it is outside add some solar cell to charge the battery. Use separate 433Mhz receiver and transmitter. Daniel i think the arduino lily (the small round one) is...

First you said 10 meters but you didn't tell us if you are using wires. If it is then the power could be provided by the cable. This is what I do. The power is provided with the cable . This way the power problem is not an issue. If it is wireless than you will need to use a contact switch to power...

i described what i need a Little better, i don't know if what you suggested is what i need

but it needs to take as less power as possible

im trying to make a raspberry pi and arduino communicate with small amount of data over 10 meters with RFID is it possible with two Mifare RC522?, and if not can you suggest something (i really don't understand RFID... yet) this is the setup i want to achieve: one raspberry does some stuff and sends...