I've been playing with some very cheap battery powered reid switches and a ninjablock at my home for monitoring doors.   It struck me that it would be a great to monitor the gates on my parents small farm block.

The max range is probably ~300m not quite free LoS though, I was wondering if anyone had any suggestions on the sort of thing that could be used to monitor gates on a farm (for a reasonable price).   Can I get away with something like 433Mhz reid switches / ninjablocks if I just get some decent aerials/weatherproofing?  Or is there a better technology?