You wouldn’t need internet access for these to work, although there is a public community WAN server you could join to operate under MQTT (which is their internet facing WAN function). They function off of LoRa RF on the 915mhz band in the U.S. (and other bands elsewhere) to do the bulk of the communication. BLE is also utilized for management.
These do need more than 1 node to operate properly, but since it works off the concept of a public mesh (with options to privatize), you don’t need two of your own devices in a developed location.
However, if no one is around or within line of sight… then you’ll have to work a little harder to get contacts/connections going.