The devices that I have seen quote 70m some 100m range with Bluetooth 4.x LE. I intend of course to take that with a very large pinch of salt. I have a number of options for placement and the devices are so cheap that I could use several to give early warning, it turns out that it would be easy to mount one right on the roadside if necessary. Some of the devices are claimed to be weather proof, which I would discount, but it in any case completely shielding one from the weather would be easy enough.
But all is to no avail without zero-hassle, zero-installation standard app support.
Burakkucat is quite right, the cattle grid is a mechanical location-based alert device. Unfortunately it doesn't compel visitors to initiate the awareness function, or start up fact recall or optical character reading services. Mrs Weaver was roaming down the road in the blackness the other night with her head-torch on, trying to find errant guests who had sailed on past, driven downhill until the satnav told them they were <somewhere random>, then found they had no 2G coverage because they had lost too much height, so had to turn round and go past (again) a mile or so up hill until they could get some phone signal to call Mrs Weaver for rescue.
I have tried to manually correct all the various well-known mapping databases so that the Mrs is not only visible but is shown at exactly the correct coordinates rather than some lazy assumption derived by the mapping software from the postcode.
Leaving aside iBeacon for a moment, it would be useful to have a way of sending people coordinates to add into an alert app (perhaps in the style of a url). It would also be useful if the mapping services could allow you to select a named location such as a business that is already shown, and generate a location alert based on that.
My problem is that I just don't know enough about Apple standard apps’ functionality, and absolutely zero about Android. With the exception of Mrs Weaver’s ancient Sony music player Android box (not even internet-connected iirc), I have never even seen an Andoid box.
I could of course just take a small risk and buy a couple of iBeacons to see if I can discover any standard apps that come to life, but I would be digging blindly at the moment.