The rain was still pattering on the roof, though the sound was a little quieter than before. Chen Hao stood at the door of the control room, holding a pair of soaking wet rain boots in his hand. The soles of the boots were covered in mud, leaving two tracks on the ground as he stepped on them.

He placed his rain boots in the corner and turned to look at the whiteboard. The sheet that read "Step 1: Demolition and Renovation – Work Starts Tomorrow" was still pasted in the middle, next to which was Nana's newly updated summary table of building material shortages. The red numbers were still glaring, especially in the cement column, where they were more than 90% short.

Susan sat at the table, her pen hovering over the line about clay, staring blankly. Carl emerged from the tool shed, a pair of rusty pliers in his hand, which he slammed onto the table with a dull thud.

“The cutting machine can’t be repaired,” he said. “The motor is burnt out and needs to be replaced.”

No one responded.

Nana's screen was lit up, scrolling through a list of material recycling priorities. She glanced up at the crowd, then looked down again to continue entering data.

The air was a bit heavy.

After a few seconds, Susan suddenly spoke up: "Can we not build the wall yet?"

Chen Hao turned to look at her: "If we don't build a wall, what if wild boars rush in at night?"

“I’m not saying give up.” Susan turned a page in her notebook. “I mean, before the wall is up, we need something to remind us, right? Otherwise, the enemy will come while we’re still asleep.”

"You want to install an alarm?" Carl frowned.

“Yes.” Susan nodded. “There are quite a few old-fashioned vibration sensors in the scrap heap, as well as several intact communication modules and speakers. We can put together a simple alarm system and hang it on the north fence. It will go off when there is any noise, which will at least buy us some time.”

Chen Hao stroked his chin: "It sounds like a security bell."

“It’s essentially the same,” Susan said, “but you can adjust the sensitivity. It won’t trigger when a person walks by, but it will sound when a large animal bumps into it.”

Carl shook his head: "The idea is good, but those sensors are all ten-year-old stuff, the signal is unstable. They alarm at the slightest sound during the day, but at night when something actually comes, they don't react at all. Who can stand that?"

“I can calibrate it,” Nana suddenly said.

Everyone looked at her.

She swiped her finger across the screen and brought up a document: "The database contains design templates for 'low-power area alert systems' that support the adaptation of older components. I can rewrite the trigger logic to filter out invalid vibrations."

"You can do this too?" Chen Hao asked.

"Electronic security is a basic engineering skill," Nana said. "The prototype can be completed within three days, and it will be put into trial use after passing the tests."

Carl was taken aback: "Are you serious?"

“The data is available.” Nana projected the plan onto the wall. “There are seven types of components needed, five of which can be found in the existing scrap materials at the base. We are missing two signal amplifiers and a backup power supply, but these can be replaced by modifying old battery packs.”

A list was projected, with the source location indicated for each item.

Susan leaned closer to look: "These things are all near the East District scrap heap. We can pick them up tomorrow."

“The problem is the soldering,” Carl said. “The circuit board needs to be redone, and I’m not confident I can do it right the first time.”

“I’ll draw the diagrams,” Susan said, opening her notebook. “You just focus on soldering.”

"You understand circuits?" Carl looked at her.

“I took an elective course in electronics practice in college,” Susan said. “Although I failed it, I still remember the principles.”

Chen Hao chuckled: "So you invented things based on your failing experience?"

“Experience comes from real-world practice.” Susan smiled as well. “Failing the exam doesn’t mean you can’t connect wires.”

Carl paused for a few seconds, then picked up the pliers and tapped them on the table: "Fine, if you guys can actually make this thing make a sound, I'll consider it a legitimate job."

"It's not about making it ring," Chen Hao interjected, "it's about making it reliable."

He walked to the whiteboard, picked up a pen, drew a blank line below the original plan, and wrote a new title: "Temporary Alert System Development Launched".

Then write in three columns: **Responsible Person, Task Content, and Time Nodes**.

"Susan is in charge of the overall design, Nana will provide technical support, and Carl will prepare for the component disassembly and soldering work." He said as he wrote, "We'll put together the list tonight and start working on it with the other recovery missions tomorrow morning. The alarm system should be deployed first in the high-risk area on the north side, which is closest to the main cabin and also the easiest place to be breached."

Susan looked at the whiteboard: "What if the test fails?"

“Then let’s revise it again,” Chen Hao said. “Anyway, we don’t have any other choice right now. The wall won’t be up anytime soon, and we can’t just sit here and wait.”

Nana nodded: "I will adjust the calculation progress of the wall materials accordingly, so as not to affect the main task."

"Can you manage all this by yourself?" Susan asked.

“I can process it in shifts,” Nana said. “The alarm system will not use more than 15% of the resources, so it won’t slow down the data collection and statistics.”

Carl stood up: "Then I'll go check if the tools are usable. If the soldering station is broken, we need to think of a solution in advance."

He walked toward the tool shed, pausing as he passed Susan: "If you can actually make a sound, I'll buy you one last can of coffee."

"Deal," Susan said. "But you have to make it yourself, don't try to fool me with hot water mixed with powder."

Carl snorted and went inside.

The room fell silent.

Chen Hao leaned against the table, looking at the component list on the projector: "What do you guys think we should name this thing if it actually comes to fruition?"

“How about we call it ‘Sentinel One’?” Susan said.

"Too formal." Chen Hao shook his head. "The electricity here is so unreliable, calling it 'make a sound' is more practical."

“Then you might as well yell ‘Help!’” Susan laughed.

Nana suddenly said, "According to historical records, early colonies often used 'Night Howl' to name their border alarm systems."

"Night howl?" Chen Hao repeated, "It sounds like a wild dog barking."

“But it can actually make a sound,” Nana said.

“That’s it,” Chen Hao decided. “When it first rings out, we’ll call it ‘Project Night Roar’.”

Susan opened her new notebook and wrote the first line: "Night Howl System Design Draft - First Version".

Nana simultaneously brought up the editing interface and began inputting parameter models. A pop-up window appeared on the screen: "Create a new project folder?"

She clicked confirm and entered the name: **Night_howl_prototype_V1**.

"A Chinese name is fine," Chen Hao said. "Don't use an English name."

“The naming has been switched to Chinese,” Nana said. “The folder name is ‘Night Howl Prototype v1’.”

Susan looked up: "What should the sensor be installed at?"

“1.5 meters,” Nana replied. “Above the ground level where weeds disturb the ground, below an adult’s shoulder, suitable for catching the approaching signals of large animals.”

"Should we add a flash?" Chen Hao asked. "Light is scarier than sound."

“It can be modified from an emergency light,” Nana said, “but additional wiring will be required.”

“Sound first, then lights,” Susan said. “One step at a time.”

Chen Hao glanced at his watch: "There are still forty minutes until dinner time. First, figure out which parts you need and give me a detailed list so I can arrange the manpower for tomorrow."

“No need to wait until tomorrow.” Susan closed her notebook. “I’ll go to the scrap heap now, take pictures and record the status of the components, so I don’t have to run back and forth.”

"I'll go with you." Nana closed some background programs. "We need to scan the component numbers on-site."

The two got up and walked outside.

Chen Hao called out to them, "Remember to wear gloves, the edges of the metal sheets over there are sharp."

“I know.” Susan turned around. “Don’t worry, I won’t test the incision with my hand.”

The rain outside was gradually subsiding, and the puddles reflected the gray sky. The two walked along the gravel path towards the east district, their shadows stretching long.

Chen Hao stayed where he was, stared at the whiteboard for a while, picked up a red pen, drew a box under "Night Howl Project", and wrote: **Today's progress: Plan established, personnel assigned, component collection expected to start tomorrow**.

He put down his pen and stretched.

At that moment, Carl poked his head out from the tool shed: "The soldering station is barely usable, but it will last for two hours at most."

“That’s enough,” Chen Hao said. “As long as they can find the parts.”

"Hopefully he doesn't bring back a bunch of scrap metal," Carl muttered, then shrank back inside.

Chen Hao was the only one left in the control room. He sat down, opened his logbook, and turned to a new page.

Just as I wrote down the date, I heard footsteps outside the door.

Susan burst in, her hair half-wet, holding a palm-sized piece of metal in her hand.

"Found it!" she gasped. "An old-style piezoelectric vibrator, model matched, interface intact!"

Nana followed behind, holding a tablet: "It has been entered into the system. Three similar components have been found, all of which are worth repairing."

Chen Hao stood up: "So, it's really possible to make it?"

“At least we have the parts.” Susan placed the metal sheet on the table. “Now it’s up to Karl to see if he dares to weld them.”

“If he doesn’t dare, I will.” Chen Hao reached out and touched the sensor. “Anyway, I’m free.”

Nana looked at them, and a notification popped up on the screen: [Night Howl Prototype v1 Project - Component Collection Phase Officially Launched]

She clicked "confirm".

Outside the window, a crack appeared in a dark cloud, and sunlight slanted across the sheet metal of the scrap heap, reflecting a brief ray of light.