Comment by serf

in a country that hostile to you I would be worried about radiating any kind of EM, honestly. It's too easy to track and could cause undue targetting & victimization.

my real answer : I think at that point in time effort is best spent trying to arrange escape.

my technical answer : depends on the scene. directed optical/laser or microwave is very hard to track if that can facilitate the links you need -- but realistically most war-time off-grid comms historically has been established via runners, dropboxes, or community radio systems ; all options with very real inherent risks.