The Space Hub has a built-in cellular modem and eSIM which allow the Airthings devices to send sensor data up to the cloud where it provides you with fresh insights. If you want to use a cellular connection, you do not have to plug in your own SIM card, all you need to do is power the Hub, and the cellular connection will be active. The eSIM is built-in, so even if you open the backplate of the Hub you won't see it.
The eSIM allows roaming worldwide with either LTE/4G (Cat-M1/LTE-M) or GSM/2G. We have a service agreement with a company called COM4, they have roaming agreements worldwide. If the Hub is placed in an environment shielded from cellular coverage (for example basements), it's possible to use an ethernet cable for local connection to the internet.