I should add that smart things used to sell a radio, called the thingshield, that you could add to an Arduino and that was very popular with maker types. But I guess there weren’t enough of those people, because they have since discontinued that device. There is a current discussion for what might be used in place of it, and that might be more of what you’re asking:
Most people seem to be switching to the ESP Wi-Fi options, which are very inexpensive, but if you go with Wi-Fi you’re going to run out of addresses fairly quickly when compared to a zigbee implementation.
Still, it’s an option to be aware of. 