Chen Hao chewed on half a flattened biscuit, staring at the red dot still spinning on the screen. He licked the crumbs off his fingers and turned up the volume on the control panel.

"This thing hasn't stopped all night." He said, his mouth still open. "When it's windy, the signal drops, and every time it drops, it jumps on the screen like it's having a seizure."

Nana stood by the control panel, her yellow LED flashing continuously. She didn't move or answer; the data stream scrolled rapidly in her field of vision.

Susan straightened up in her chair and rubbed her neck. "You woke us up because of this?"

“It’s not because of me.” Chen Hao pointed to the screen. “It’s because every time it loses a packet, it happens exactly when the wind speed exceeds eight meters per second. I’ve recorded it three times, and each time it was off by less than a second. This is no coincidence.”

Carl leaned against the wall, still clutching the rusty chisel from last night. "You mean the wind's too strong, and the antenna can't withstand it?"

“I think it’s because there aren’t enough repeaters.” Chen Hao handed over the tablet. “Look at these nodes. The seventh probe on the east side keeps disconnecting, but the others are working fine. It’s the one furthest from the main box, and there’s no amplifier in between.”

Susan took the tablet and looked at it for two seconds before frowning. "The three relay points we set up are all in the south and west, there's definitely a gap in the east."

Nana finally spoke up: "The knowledge base suggests adding an anti-interference relay module and using a frequency hopping communication protocol. However, the current power load is already at 89%, and the new equipment will require a redistribution of power."

“Then let’s dismantle something else,” Chen Hao said. “Anyway, the alarm system doesn’t need the lighting linkage right now, so let’s switch the power over there for emergency.”

“No,” Susan shook her head. “The lighting is on a backup circuit, so we can’t touch it. But we can reduce the bandwidth of the kitchen surveillance cameras. All four cameras over there are just filming empty hallways, and all they do all day is watch mice running around.”

"Then hurry up and cut it." Chen Hao plopped back into his chair. "I don't want to be caught in a strong wind next time and not even know if an elephant is charging at us."

Susan started typing. Carl put down his chisel and turned to rummage through his toolbox. "I'll go check the east end of the building to see if the antenna is crooked; it's easy for it to tilt if the wind blows on it for too long."

"And bring the new repeater box along with you." Susan said without looking up. "I'll write the program later, and you can install it on-site."

“We need to add a voltage regulator cable.” Carl pulled out a section of shielded cable. “Otherwise, if the voltage fluctuates, the module will burn out on its own.”

Chen Hao was hunched over the control panel, his eyes glued to the screen. "Once you guys are done, I'll go try setting a fire again."

"What are you going to burn again?" Susan asked.

“Haystacks,” he said. “It worked when we tested animal sensing last time. This time, let’s add temperature changes and see if the system can detect movement and heat sources simultaneously.”

"Don't get too close," Susan warned. "You almost melted the probe last time."

"I know," Chen Hao waved his hand. "I know what I'm doing."

Two hours later, the sound of a walkie-talkie came from the eastern probe area.

"The repeater box is installed." It was Carl. "The antenna angle is adjusted to forty-five degrees and fixed."

"Is the power on?" Susan asked.

"It's been accepted. Voltage stabilization has also been done, using connectors wrapped in melt-coated tubing, so it's not afraid of rain."

What is the signal strength?

After a brief silence, Karl reported the number: "Eighty-two percent, stable."

Susan tapped on the terminal, and the new node appeared in the topology graph. She pressed the synchronization button, and all devices began to re-handshake.

Chen Hao leaned closer to look at the progress bar. "Is it done?"

"Not yet," she said. "The way the data is packaged needs to be changed. Right now, we're sending everything at once, and it gets congested when there's a strong wind. I need to split it into smaller packets and add an automatic retransmission feature."

"It sounds like parcel sorting," Chen Hao said.

“Pretty much.” Susan’s fingers never stopped moving. “If one package is lost, the others will still arrive. It’s better than the whole batch being stuck in transit.”

Nana suddenly raised her hand and projected a stream of code into the air. "It is recommended to use a sliding window mechanism, which can dynamically adjust the retransmission frequency. The current average network latency is 320 milliseconds, so setting the window size to eight is reasonable."

“Okay.” Susan simply copied and pasted the code. “You’re in charge of calculating the threshold, and I’ll write the API.”

Chen Hao yawned, stood up, and stretched. "You guys take your time, I'm going to take a leak."

When he returned, the alarm panel on the main control panel had turned green.

"So fast?" he exclaimed, his eyes wide.

"We just completed the final transmission test." Susan looked at the screen. "No packet loss for ten consecutive minutes, and the latency remained stable within 300 milliseconds."

"Then why don't we hurry up and test the functions?" Chen Hao rubbed his hands together. "I'll go to the east end and set a fire. Karl will come with me to make some noise."

"Wait a minute," Susan stopped him. "The logic module isn't working properly yet. What happened just now was only a pathway; it doesn't mean it can issue an early warning."

"Then what are you waiting for?" Chen Hao said, "Get it done."

Nana's eye light flashed more frequently. "The judgment algorithm is being reconstructed. A dynamic threshold is being introduced: when the vibration in a certain area increases and the temperature rises by more than five degrees, a level two alert is triggered; if it continues for more than ten seconds, it is upgraded to level three."

“What about a tiered response?” Susan asked.

"Level 1 records only, level 2 flashes lights, and level 3 sounds an alarm," Nana said. "The audio and visual signals have been integrated into the citywide broadcast system."

"That's enough." Chen Hao grabbed his coat. "Let's go, let's test it in real combat."

Ten minutes later, a metallic clanging sound came from the eastern probe area. Then, a small plume of black smoke rose up.

The control panel went off instantly.

The red light flashed, the horn blared, and a pop-up window appeared on the screen: "East District Anomaly! Severe vibration and localized temperature rise detected! Risk Level: Level Three!"

Susan stared at the data stream. "Timestamp matching, accurate location, response latency of 340 milliseconds."

"Perfect!" Chen Hao shouted into the walkie-talkie. "One more time! This time I'll kick the wall!"

In the second test, the system successfully triggered the alarm again.

The third time, they switched to the west area to simulate the approach of large organisms in the low-temperature environment at night, and the system still responded promptly.

Back in the control room, Chen Hao plopped down and grabbed his water bottle, taking a huge gulp. "Is it really working now?"

“It’s basically stable,” Susan nodded, “but there’s still one problem.”

"What?"

"During the third test just now, the system misjudged a tree shadow as swaying," she said. "The infrared image was blurry and was mistaken for a moving heat source."

"Then let it see more clearly," Chen Hao said. "Why not just add a camera?"

“It’s not that simple.” Susan frowned. “A single sensor is prone to false alarms. We need to do fusion recognition—infrared and visible light, double confirmation before triggering an alarm.”

“Okay,” Chen Hao said. “Then add it. All I want to know right now is—can this thing even be used?”

Nana's eye light changed from yellow to blue and then returned to constant light. "The video fusion module has been loaded. After 48 hours of continuous operation testing, there were no missed reports, and the false alarm rate dropped to 0.3 percent."

Susan took a deep breath, her finger hovering over a button on the main control panel.

"Ready?" she asked.

"Go ahead and press it," Chen Hao said. "I've gained five pounds waiting for this day."

She pressed the confirm button.

The alarm panel turned from yellow to green, and a steady "beep" sounded, silencing the entire room for a second.

"The system is online," Susan said softly.

Chen Hao grabbed the microphone, his voice trembling slightly: "Attention everyone, the alarm system is now fully activated. We really do have 'eyes' now."

No one responded, but Carl smiled, Susan relaxed her shoulders, and Nana's eyelight remained steadily lit.

Chen Hao put down the microphone, picked up the tablet, and began to browse through the test records. His finger swiped across the last column of logs and stopped at a marker.

“Strange,” he said.

"What?" Susan asked.

“Look here.” He turned the screen toward her. “At 3:17 a.m., the system recorded a slight vibration, located outside the northwest corner of the wall, lasting for eight seconds, with a very low amplitude.”

"Wind?" Karl guessed.

“It doesn’t seem like it.” Chen Hao shook his head. “Wind doesn’t cause directional vibrations. And…” He paused, “the wind stopped then.”

Susan leaned closer to examine the data. "No video recordings?"

“The camera didn’t trigger,” Chen Hao said, “because it didn’t reach the alarm threshold.”

Nana's eyelight flickered slightly. "I can retrieve the original sensor data for retrospective analysis."

"Investigate," Chen Hao said. "Pull out that waveform for me."

Nana stood still, while light patterns swirled rapidly inside the lens. A few seconds later, a waveform was projected onto the ground.

Chen Hao squatted down to take a look. "This curve... is not right."

"Is there anything unusual?" Susan asked.

“It looks like…” Chen Hao pointed to the crest of the wave, “It’s regular. It happens every 1.2 seconds, seven times in a row, and then it stops.”

Carl scratched his head. "Who's keeping time outside?"

“It’s not human,” Chen Hao said in a low voice. “A human wouldn’t tap the ground at this frequency.”

Susan stared at the waveform for a long time. "Should we send someone to check it?"

“No.” Chen Hao stood up. “Going there would only alert them. Have Nana keep an eye on this spot, and if the same signal appears again, mark it and record it immediately.”

“Monitoring tasks have been set up,” Nana said.

Chen Hao walked to the window and looked towards the northwest wall. He couldn't see anything there, only the wind blowing through the weeds.

He put his hand into his pocket and felt a hard, crumbly biscuit.

"Tomorrow," he said, "move the nearest camera five meters over there."