The observation modules are a relic from the old wars. It served as an early warning system for Helvetia. It is unknown how the box functions because there is no maintenance access panel
The observation modules served as an early warning system for Helvetia. It is highly likely the module has a built-in Identification Friend/Foe (IFF) system as indicated in Episode 11 when one of the modules flickered when Roman soldiers passed by.
It is possible that each observation module has a self-sufficient power generator, allowing it to function for years and in this case, decades. This freed up troops that were needed to replace the greivous losses at the front.