As soon as it was light, Chen Hao was woken up by Nana before he was fully awake.
“The alarm went off again,” she said. “At 3:17 a.m., it lasted for four seconds, with no triggering source.”
Chen Hao rolled over and pulled the pillow over his head: "Let it make a sound, anyway, no one's going to steal our pile of broken bricks."
“That’s not the point.” Nana stood by the bed, her voice neither loud nor soft. “The point is that it makes a sound when it shouldn’t, and it doesn’t make a sound when it should.”
He lifted the pillow, squinted at her, and asked, "Did you stay up all night again last night modifying code?"
“I can’t sleep,” she said. “My system doesn’t need rest.”
“But you need to let people rest.” Chen Hao sat up and scratched his messy hair. “Karl carried bricks all day yesterday, and Susan’s eyes were red. If you sound the alarm now, they’ll think wild boars have invaded.”
Nana didn't say anything, but simply pulled up the alarm record from last night and projected it onto the wall. A waveform appeared, with minimal fluctuations, as if someone had gently touched the fence.
"It was the wind," Chen Hao said.
“Eighty-two percent chance,” Nana nodded. “But the system can’t distinguish between wind, small animals, and potential threats, so it triggered the highest response level.”
“Then don’t make it so sensitive.” He yawned. “Just like people, being too nervous makes you prone to making mistakes.”
Nana turned to look at him: "You suggest lowering the sensitivity?"
“It’s not about lowering it, it’s about being a little smarter.” He scratched his neck. “For example… just note down the small noises, and only call out for the big ones.”
“A tiered response mechanism,” Nana immediately added. “There’s a similar design in the database.”
Chen Hao waved his hand: "Don't use technical terms, I'm a terrible student, I don't understand them."
"I know what to do." She said, then turned and walked away, her steps steady, without looking back.
Chen Hao lay back down, stared at the ceiling for two seconds, then got up again: "Wait, are you going to make changes?"
Her voice came from outside the door: "It's already being done."
He quickly put on his shoes and chased after them.
The small table in the control room was piled high with disassembled circuit boards. Susan was using tweezers to pick up a thin wire, her forehead covered in sweat. Carl sat against the wall, clutching a half-empty bottle of water, his eyes glazed over.
"When did you guys start?" Chen Hao asked.
“She knocked on the door at four o’clock and called me here.” Susan said without looking up, “She said she had a new plan and insisted on trying it now.”
“I couldn’t stop her,” Carl muttered. “She was standing at the door, and she wouldn’t leave unless I went to her.”
Chen Hao looked at Nana: "Can't you wait until dawn?"
“The problem won’t disappear on its own,” she said. “The sooner it’s resolved, the less it will affect subsequent arrangements.”
"But people can break down."
“People can take turns.” She pointed to two modules on the table. “This one is responsible for monitoring weak signals, recording them without triggering an alarm; this one is responsible for capturing large displacements, triggering an audio-visual alert only when a threshold is reached.”
Susan finally looked up: "The principle is like a heart monitor; you watch the curve normally, and it only sounds when there's an abnormality."
“Yes.” Nana nodded. “We use piezoelectric ceramics as the sensing layer and metal foil as the conductive path. It’s low-cost and moisture-resistant.”
“That sounds pretty promising.” Carl slowly stood up. “But can the power supply hold up? The last version ran out of power in the middle of the night.”
“This time, the power supply logic has been changed.” Nana opened a diagram. “Normally, the main system is in sleep mode, and only the standby module is running, consuming less than one percent of the power. Once continuous vibration is detected, the main controller is immediately woken up.”
"It does save power," Susan frowned, "but is the wake-up speed fast enough?"
"The actual delay is 0.6 seconds," Nana said, "from signal recognition to full activation."
Chen Hao whistled: "You got up even faster than me."
Carl grinned. "Then don't stay in bed late anymore, and let the alarm ring for you."
"Stop arguing." Susan picked up the welding torch. "Let's make this prototype first."
The three of them busied themselves around the table. Nana was in charge of wiring, her movements precise, each wire fitting perfectly into its corresponding slot. Susan soldered the joints, her fingers steady as if she hadn't stayed up all night. Carl handed over tools and, incidentally, grabbed an old monitor to convert into a surveillance interface.
With nothing else to do, Chen Hao drew a little figure next to the box and stuck it on, writing three words: **Don't make any noise**.
The first prototype was assembled before noon.
"The test site is set in the open space in the west area," Nana said. "The wind is strongest there, making it the easiest to accidentally trigger something."
They secured the device to the fence post, connected the battery, and turned it on. The indicator light flashed three times before turning a soft green light.
"Enter standby mode," Nana announced.
"What do we do now?" Carl asked.
“Wait,” she said. “Or, create artificial interference.”
Chen Hao picked up a tree branch and swung it from a distance, hitting the fence.
With a snap.
The device light turned yellow, the buzzer beeped twice, and a message appeared on the screen: **Slight vibration, recorded**.
No one called the police.
“That’s good.” Susan nodded.
Then, Carl went around to the other side and suddenly slammed into the iron fence. There was a loud crash.
The red light immediately flashed, the beeping sounded prolonged, and a mechanical female voice came from the loudspeaker: "High-intensity intrusion detected, please handle immediately!"
"Quick reaction time," Chen Hao laughed. "Even more eager to run than I am."
“Let’s try again,” Susan said. “Let’s see how it goes.”
For the next two hours, they took turns throwing stones, slapping the wire mesh, and running past it at high speed. The equipment recorded seven minor disturbances, but only two triggered real alarms, both because Karl went too far and directly pulled at the barbed wire.
“Basically met.” Susan closed her notebook. “The false alarm rate has been reduced, and the response has been timely.”
"How much of the battery did you use?" Carl asked.
Nana checked the data: "Total power consumption is nine percent, of which six percent was used for three complete alarms."
"It can last a week," he said, "if no one's banging their head against the wall every day."
"So it's approved?" Chen Hao looked at Nana.
“Preliminary verification complete,” she said. “I can generate configuration files in batches to guide the next installation step.”
"Is it my turn to work?" Carl stretched his shoulders. "It should have been like this a long time ago. My legs are numb from standing and watching for too long."
Susan smiled as she packed her things: "I didn't expect it to actually work."
“I said it would work,” Chen Hao said, leaning against the railing. “Although I don’t know why.”
“Because Nana is smart.” Karl patted her shoulder. “Better than us bunch of chubby-headed people.”
Nana didn't laugh, but when she saved the last line of code to the memory card, she added a note: **Version Naming: Don't call it number one randomly**.
It was three o'clock in the afternoon, and the sun was blazing.
The four men returned to the open space outside the tool shed. On the table sat three newly assembled sirens, their casings coated with rust-proof paint and all the joints sealed.
Nana was explaining the installation sequence and wiring method to Carl. Susan checked the list, occasionally interjecting with a note of precaution. Chen Hao squatted nearby, sanding down a loose bracket.
“Five points on the north side and three on the south side,” Nana said. “Priority will be given to covering entrances and low-lying fence sections.”
"Understood." Karl put on his gloves. "Should we install the north side first?"
“Yes.” She handed over the waterproof box. “The first checkpoint is fifteen meters from the starting point, avoiding the areas that were flooded yesterday after the rain.”
Do you still remember that place?
“I remember all the abnormal terrain data.”
Chen Hao handed the repaired bracket to Karl: "Here you go, don't install it crookedly."
"Just mind your own business." Karl took the box, lifted it, and tested its weight. "It's quite heavy."
“There are spare batteries inside,” Nana added. “Each unit comes with two sets, which are used alternately.”
Susan closed her notebook: "Once all these are installed, at least I can get a good night's sleep."
"Not necessarily." Chen Hao stood up. "What if it really does ring?"
“That means someone’s coming.” Carl stepped outside. “We’ll see if you can run faster or if the alarm goes off faster.”
Nana did a final check of the program loading status. A green checkmark appeared on the screen, indicating: **Deployment ready**.
She removed the memory card, put it in a waterproof bag, and handed it to Carl.
Carl took the card and turned to walk towards the north fence.
Chen Hao watched his retreating figure and suddenly called out, "Hey!"
Carl stopped.
"What if someone really comes..."
"What's wrong?"
"Bring some food."
Carl rolled his eyes and continued walking.
Nana stood still, watching the indicator light on the device change from green to blue.
Susan packed away her toolbox and brushed the dust off her knees.
Chen Hao felt the half-eaten biscuit in his pocket and took a bite.
The wind blew in from the west, carrying a hint of dust.
Carl walked to the first burial site, put down the box, and unlocked it.
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