When the terminal emitted a short beep, Chen Hao was staring blankly at the 86.7 points on the screen. The number felt like a branding iron, making his eyelids twitch.

"The western line sensor signal is interrupted." Nana's voice was flat.

Carl opened his eyes, his head still against the wall. "It broke again?"

“It’s not a temporary malfunction.” Nana swiped her finger to bring up the backup monitoring screen. “The main power supply is normal, but the signal is blocked.”

Susan leaned closer: "Is the equipment old?"

“No.” Nana shook her head. “The infrared heat source detected a moving target, three to five people, approaching the outside of the wall.”

The air in the room suddenly felt heavy.

Chen Hao stood up and walked to the control panel. "Can you see what it looks like?"

"The distance is too far, and the image is blurry." Nana zoomed in on the image, where dust rose in the distance and several shadows swayed in the sandstorm. "But judging from their pace and path selection, they don't look like animals."

"Someone's coming?" Carl sat up straight. "Who would come this way?"

"I don't know." Chen Hao stared at the few blurry figures, "but no one would come on a picnic in the middle of the night."

Susan opened her notebook. "We only put the alarm system on level one response after our last drill. Before that, nobody paid any attention to what was happening outside."

“So—” Karl said slowly, “they may have already seen us several times?”

No one responded.

Nana suddenly spoke up: "The other party is carrying a metal object, and the reflected waveform analysis shows that it is a tool or weapon."

“Weapons?” Susan paused, her pen twitching. “You mean, they brought weapons?”

“The purpose cannot be confirmed at the moment,” Nana said, “but the behavioral patterns are similar to those of the homeless community.”

“Wanderers?” Karl smiled wryly. “I thought those were just legends.”

“Not anymore.” Chen Hao grabbed a water bottle from the table and took a swig. “We just thought we were pretty sturdy, and then a bunch of guys came in wanting to tear down the wall.”

“But we didn’t provoke them,” Susan frowned. “What if they were just passing by?”

“They won’t head straight for the water source area when they pass by.” Nana marked the other party’s route. “There are water storage tanks and water purification devices on the west side of the base, which is the only water supply point. Their direction is very clear.”

“They’re after the resources.” Karl stroked his chin. “They’ll either steal them or borrow them.”

“You have to ask permission before you borrow.” Chen Hao put down the bottle. “Approaching without prior notice is a threat.”

“What if they are survivors?” Susan’s voice lowered. “Maybe they are also looking for a place to stay.”

“You can settle down, but knock before you come in.” Chen Hao pointed to the screen. “But they’re acting like they’re on reconnaissance, taking one step and stopping the next, deliberately going around blind spots.”

Carl suddenly chuckled: "Do you think they might be having a meeting too? 'Brothers, there's a base up ahead, should we make our move tonight or tomorrow morning?'"

"Possibly." Chen Hao didn't smile. "So we need to figure out how to reciprocate first."

Susan closed her notebook: "Can our defense system... handle this kind of situation?"

The room was quiet for a few seconds.

Nana began, “The existing system is designed based on natural disasters and mainly deals with sudden environmental changes and wildlife intrusions. It lacks specific plans for the intelligence, collaboration, and destructive intentions of human groups.”

“In other words—” Carl shrugged, “the wall can prevent a collapse, but it can’t prevent someone from picking the lock?”

“Accurate.” Nana nodded.

"Damn it." Carl leaned back against the wall. "We've been working so hard on this for ages, and the key is still floating outside?"

“It’s not just the door.” Chen Hao looked at the radar chart. “When the alarm goes off, we know to run; when the water pipe bursts, we know to fix it. But the problem now is, if someone is going to break down the door, we don’t even know whether we should open it or not.”

"So what do we do now?" Susan asked.

"Let's clarify a few things first," Chen Hao said, holding up a finger. "First, how long until they arrive? Second, what methods do we have at our disposal? Third, if a fight really breaks out, who can step in?"

Nana has already begun operations: "Based on the movement speed, we expect to enter the warning area in 43 minutes. Currently available resources include: perimeter lighting system, audible and visual alarms, surveillance cameras, emergency broadcasts, and underground escape tunnels."

"No offensive equipment?" Karl asked.

“No,” Nana said. “The original plan did not include an external defense module.”

"So all we can do is scare people?" Carl grinned. "Shout 'Closed' through a megaphone?"

"That's how it is for now," Chen Hao said. "But we have an advantage."

"What?"

“We’re inside, they’re outside.” Chen Hao pointed to his head. “And now we know where the problem lies.”

“Knowing where the problem is doesn’t mean we can solve it,” Susan cautioned. “We don’t even know how many people the other side has.”

“Let’s start by thinking about the worst-case scenario.” Chen Hao turned to face the three of them. “If they’re here to steal, how do we defend ourselves? If they try to force their way in, how do we stop them? If they pretend to ask for help to trick us into opening the door, how do we see through their deception?”

“This…” Carl scratched his head, “I only know where to run during drills.”

“This is not a drill.” Chen Hao looked at him. “Those figures just now were really walking this way. We can’t wait until they knock on the door before we think about fixing things.”

Susan whispered, "We were only thinking about how to survive, not how to protect ourselves from others."

“Now we need to think about this.” Chen Hao walked to the map. “No matter how high the wall is, it can’t stop people from digging tunnels at night. No matter how loud the alarm is, it can’t stop a group of people from rushing in together. What we lack is not bricks, but brains.”

“You mean…we need to change our defensive strategy?” Carl asked.

“We must change,” Chen Hao said. “In the past, we defended against natural disasters; now we have to defend against man-made disasters. This is not an upgrade; it’s a change in thinking.”

Nana added: "It is recommended to immediately activate the potential intrusion warning mechanism, shut down unnecessary external devices, lock the backup power supply, and activate remote monitoring patrol."

"Let's do it," Chen Hao decided. "Do as she says."

Susan began recording the instructions, Carl got up to check the distribution box, and Nana's fingers flew across the screen.

Chen Hao stood in front of the control panel, his eyes never leaving the moving red dots.

“They brought tools,” he muttered to himself. “That means they came prepared. These kinds of people don’t go back empty-handed.”

“Maybe they just want to negotiate.” Susan looked up.

“We can talk, but we have to talk at the place we’ve chosen,” Chen Hao said. “It’s not the time they chose, nor the rules they set.”

"You want to take the initiative to make contact?" Karl turned around.

“No.” Chen Hao shook his head. “We won’t move. Let them know that this place is in charge and not to be trifled with, that’s enough.”

“But we didn’t even give them a warning,” Susan frowned. “We can’t just wait until they climb over the wall before we call a halt, can we?”

“Then let’s add a step.” Chen Hao looked at Nana. “Could we play a message automatically when they get close? Like ‘You have entered the monitored area. Please evacuate immediately.’”

“It’s technically feasible,” Nana said. “I can connect to the broadcast system and set the trigger distance.”

“Add a scary tone,” Carl interjected. “Just say, ‘Infrared lock is on, next step is to release electricity,’ to intimidate them.”

“No need to make up lies,” Chen Hao said. “Just tell the facts. We have surveillance cameras, alarms, and guards. Let them know this isn’t lawless territory.”

"Will this work?" Susan asked skeptically.

"Not necessarily," Chen Hao admitted, "but at least we're making our stance clear. We're not afraid of trouble, nor are we welcoming it, but we will absolutely not let anyone step in our way."

Carl sighed: "So, we just thought we were a regular army, only to find out we didn't even have any sentry posts?"

“It’s not too late to set it now,” Chen Hao said. “The problem is that we always thought the biggest danger was a building collapse and power outage, but we forgot that the most troublesome thing is never the sky collapsing, but someone trying to lift your roof off.”

"What will you do then?" Susan asked. "Will you have to get nervous every time you see someone?"

“Not every time.” Chen Hao looked at the screen. “From today onwards, we must treat ‘human beings’ as a disaster to be prevented. More unpredictable than earthquakes, more ruthless than fires, because they can think.”

No one spoke inside.

Nana said softly, "The new model is loading. After adding the human threat variable, the defense score is expected to drop by twelve percentage points."

"Let it drop then." Chen Hao smiled. "Good scores are useless; only survival matters."

Carl leaned against the wall, watching the increasingly clear figures on the surveillance screen.

“This time…” he murmured, “it’s not a drill.”

Chen Hao didn't respond. His fingers were tapping slowly on the table.

The red dot on the screen continued to move forward.

There are still 3,200 meters to the warning line.