You need to be careful with long range radio solutions. Radio waves sources are very easy to locate with cheap equipment. Wifi/Bluetooth is perhaps better since it's already everywhere, but the range isn't good.
Watch out, Wifi and Bluetooth and any radio source can be located (with direction finding, Time Difference on Arrival, ...).
It's sometime a bit more difficult: with spread spectrum technologies for example, widely used wireless technologies that work well in dense usage. It works also on cellular networks (2G, 3G, 4G, 5G).
Just so people don't get a false sense of security with some solutions.
Thanks, I'm aware of that - that is why I was thinking about low cost (say cost of Raspberry Pi) and distributed. When it is low cost - there is grater chance that large number of nodes can be deployed and single point of failure can be avoided.
It's sometime a bit more difficult: with spread spectrum technologies for example, widely used wireless technologies that work well in dense usage. It works also on cellular networks (2G, 3G, 4G, 5G).
Just so people don't get a false sense of security with some solutions.