[TaylorAlexander]

Some kind of LoRa radio would do well. This 433 mhz one would have long range with a bidirectional link.

https://www.adafruit.com/product/3179

[GordonS]

Haven't heard of LoRa before - is it some kind of alternative to zigbee?

[MrMid]

It has been presented to me as an alternative to GSM. It's short for Long Range. They marketed it as a product for smart city, not smart home.

But of course that doesn't mean you can't use it that way.