If it weren't for Qi Lin's extra attention, I'm afraid he wouldn't have been able to discover the Morse code hidden in it, let alone others.

Without a dedicated audio analyzer, or a skill like Qi Lin's ability to push perception and endurance to the limit by accelerating the concentrating vortex, no member of the Thunder Falcon team would be able to detect the hidden information after receiving this buzz.

Since it is a survival signal, it should be concise and easy to understand, only in this way can people understand it at a glance - like those survivors who are stranded on isolated islands, if they want to put a distress sign on the beach, it must be bigger and more eye-catching, the better, there is no reason to put a distress sign and find a way to cover it up......

Unless......

Unless the person seeking help is in some kind of dangerous situation, and no one else can see the distress signal?

It's like those spy movies, the agents who go behind enemy lines?

This explanation seems to work, but if that is the case, the distress signal should not be sent on the FM radio channel at all, which is not an encrypted channel in the first place, not only has a short transmission distance, but is also extremely easy to intercept...... As for cracking, all you need is an audio analyzer.

Feed this beep into an audio analyzer and you'll easily see a frequency curve of three lows sandwiched between six highs, and even the most stupid person can see that it's an international distress signal.

……

……

While sneaking, Qi Lin thought about this distress signal, and unconsciously touched the outside of the Leshan City Garbage Treatment Plant.

Facilities like the garbage treatment plant are naturally built on the edge of the city, but when Qi Lin walked into this garbage treatment plant, he found that it was extremely clean, as if it had been emptied.

Even on the eve of the outbreak of nuclear war, most of the people fled the city, and the number of people left behind was definitely not small, and the amount of garbage produced in a city of millions of people on that day was a very large number, and there was no reason why the garbage treatment plant would be empty.

Qi Lin walked around the inside of the garbage plant's walls, and he soon noticed an anomaly - the ground of the garbage dump seemed to be empty......

There is no shelter underground in Leshan City, and even if there is, the minimum standard for a nuclear shelter must be more than five meters underground, but judging by the echo from the knocking on the ground, it seems that there is a huge underground space less than one meter below the garbage dump.

The original dump did not have a basement, and the garbage transported here was sorted and the recyclable part was sent to other places for disposal, while the non-recyclable part was incinerated or transported to the suburbs to be dug for landfill.

It's too close to the city to be incinerated or landfilled, and the garbage dump is just a rudimentary sorting process.

Qi Lin quickly found the entrance to the underground, which was located at the back of the garbage dump, a four-meter square opening, with a square metal cover with a pull ring on the surface, and there was no cover or camouflage around the entrance.

Previously, the recovery team quickly withdrew from the ruins of Leshan City after finding the corpses, and did not stay in it for a long time, and they did not come to this garbage treatment plant.

There was no lock on the metal cover, although it was heavy, but it was not a problem for Qi Lin, he clamped the gun under his arm, and with a light lift of his hands, a step leading to the ground appeared in front of him.

At the same time, a strong strange smell also emerged from inside.

This strange smell is very special, it seems to be mixed with a variety of volatile chemical reagents, Qi Lin can't tell what ingredients are in it, to be on the safe side, he still took out the gas mask and put it on his head.

Then, he took out a lighter.

This is not to detect the presence of breathable oxygen in the underground space - his gas mask is fully enclosed, and the oxygen required is generated by the reaction of the oxygen generator in the reaction tank, and he does not need to rely on outside oxygen at all, he does this only to test whether there is flammable and explosive gas in the basement.

There are many kinds of volatile chemical reagents whose properties are extremely unstable, among which there are countless types of flammable and explosive, if this gas is mixed with one or several such substances, as long as Qi Lin dares to shoot in the basement, or accidentally rub a small spark, I am afraid that what awaits him is an extremely violent explosion.

The explosion that occurs in the confined space underground is much more powerful than the open area on the ground, and if it were to do so, it would be completely cool.

The flame of the lighter was normal, neither extinguished nor exploded, Qi Lin simply threw it directly under the steps, and nothing happened.

The danger of explosion was temporarily ruled out.

Turning on the safety of the large-caliber assault rifle, Qi Lin held the gun in one hand and a stun bomb in the other, and walked down the steps step by step.

The basement is not very deep, about five meters high, and the top is about one meter above the ground, but the space is very spacious, almost 1.5 times the size of the garbage treatment plant directly above, which is 4 to 500 square meters.

The vault, walls and floor of the basement are made of poured concrete, with a mesh wire fence in between which areas of various sizes are arranged in canvas-wrapped cabinets.

Qi Lin picked up the lighter, and when he bent down, he found that there were many two-centimeter-wide wheel rut marks on the concrete floor in the basement, which he estimated should have been left by some kind of transportation when carrying these cabinets.

Quietly approaching the nearest area, pushing open the unlocked partition door, Qi Lin walked to a cabinet.

It wasn't until recently that he found out that it was not a canvas wrapped in these cabinets, but a synthetic fiber with a very special texture, very thin, but very tough, and he cut it with a dagger for more than ten seconds before he finally cut a palm-wide hole on it, and it took a lot of effort to tear the hole wide enough to expose the entire cabinet.

The cabinets are made of metal, not painted, without any markings and, of course, not locked.

Qi Lin hesitated slightly, then directly opened the metal cabinet, and the moment the cabinet was opened, a cold air immediately hit his face-

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