I have a simple arduino system set up at around 50m away that is connected to an external power supply and it is out of sight. I would like to be able to switch the system on and off remotely. How could I do this?
I thought about using a second board and connect the two with RF transmitters and receivers, RF modules are not locally available where I am from. Are there any alternatives?
If there is power at the remote end, as you have said, you can use a transceiver such as the nrf24L01. The receiver would be at the "out of sight" end and would be permanently powered, ready to respond to a signal from the transmitter, say switching on and off various circuits etc.
If the remote end is battery powered only, or there are other reasons you wish to preserve power, then you have to look at other solutions.