Thanks for the reply.
I think Bluetooth could be envisaged with such a distance, especially with BT5.0 (BLE). However, it seems that people often have trouble with BT on the Jetson Nano (see e.g. this thread or this thread). That’s one of the reasons I was asking my question in the first place, to see if alternatives have been found by others.
As mentioned above, regarding timing, a delay of a few seconds is acceptable (let’s say up to 5 seconds). There would be at most one trigger every minute, and there is not much information to be sent (just a on/off signal). The system could be deployed in a rather isolated location, hence I cannot assume that an external WiFi router would be available.