"South City? Reinforcements?"
Above the massive Land Fortress, the Bearded Man turned around and looked at the officer beside him. "What does that mean?"
"We only received those words. There was no further information."
The bespectacled man beside him, apparently a technical officer, answered slowly, "Perhaps he was warning us to watch out for South City's reinforcements?"
"Was this message sent by our inside line in the city?"
The Bearded Man frowned slightly and continued, "How was it sent?"
"The principles involved may be somewhat complicated to explain."
The technical officer raised his head and looked at the silent, towering wall ahead, at the lights on it illuminating the ground below.
"The military lights on walls like these have stringent technical requirements. Their brightness can be adjusted continuously, and even the slightest adjustment is imperceptible to the naked eye, but our detection equipment can pick it up.
"Based on that feature, we can transmit information by controlling slight flickers in the lights. For example, high brightness represents 1 and low brightness represents 0, forming complex codes that can be translated. Of course, the actual brightness has more than two settings, so the algorithm is more complicated.
"The communication device in that inside line's hands basically works on this principle.
"That device can connect to the internal network of the city defense system, interfere with the lights' flickering, and transmit intelligence to us through those flashes. Since it isn't connected to the core communication equipment, it is less likely to be discovered by the city defense system's Artificial Intelligence or software engineers, allowing for covert communication."
"So he can send us information through the lights?"
The Bearded Man glanced up at the lights on the wall. "But why did he send only one word?"
"We don't know either."
The technical officer