Signal transfer up to 5Km

I need to transfer digital signal up to 5Km away as quick as possible. Can anyone suggest me best communication solution?
Digital input on side 1 must set my digital output on side 2.


Any idea is welcome,

Regards,

Joze

What type of digital data?

WiFi with directed antennas can go over that range on high speed.

First thanks for your fast answer TPetar.
I have 5 volt digital input on my arduino microcontroller, which must be transfered to other location.

You can try ZigBee.

http://www.digi.com/xbee/

Yes, I examine this product before.
The only negative thing here is a price. I need this two modems for skiing stopwatch.
Digital input on my arduino on one side will start stopwatch at the end.