03.07.2023
Android app for signaling does not work. Car alarm. Interpretation of the data obtained
Let's create new scheme(for example, under the name radioaudi-reversing.grc), where the signal will no longer be taken from bladeRF, but from a recorded file. To do this, we use the File Source block, to which we simply pass the file name. Now the fun begins. When converting the “picture” obtained at the previous stage (Fig. 2) into the dependence of the signal level on time, its value is taken as the sum of all amplitudes over all covered frequencies of the spectrum for each moment in time, therefore the signal under study must be separated from the noise. To do this, you can use the Low Pass Filter module, but it cuts off the frequencies, leaving a corridor around the zero frequency, that is, exactly in the center (0 MHz).
In any case, in the center we have a signal from DC in the electrical circuit of the device, and changing the freq parameter will not solve the problem. But the entire spectrum can be shifted by multiplying the signal coming from the osmocom Sink by another, with a frequency equal to the required shift (this is mathematics). To do this, we will add a Multiply and Signal Source block; we will feed the signal of the second to the input of the first along with the output of File Source. The Multiply output, in turn, will be passed to the Low Pass Filter. Here I chose a cutoff frequency of 10 kHz (value 10e3) and a transition width of 1 kHz (value 1e3, this parameter determines how sharply the filter cuts the signal, that is, how blurry the edges of the boundary region are).
Another important parameter is the Signal Source frequency - the value by which the existing signal will be shifted. It makes sense to place it on the workspace with a slider, just like freq, under a name, for example, freq_0. Now we simply direct the Low Pass Filter output to the WX GUI Waterfall Sink - the useful signal should fall exactly in the middle, at a conventional frequency of 0 MHz.
Hooray! At this stage, we can already get close to signal analysis. Let's drag the WX GUI Scope Sink onto the workspace and connect it to the Multiply output through the Complex to Mag block, which serves, as you might guess, to transfer signal values from the complex region to the region of real values that are more convenient for operating. In Fig. 3 you can see how it should look.
Fortunately, our data is transmitted using amplitude modulation and there are only two levels, so we can go straight to the binary representation. To do this, let's direct the Complex to Mag output to the Binary Slicer block, which converts the sequence of signal amplitudes into a sequence of zeros and ones, depending on whether the value is greater than zero or not. Since all of our signal amplitude values are greater than zero, using a simple arithmetic block Add const with a value of approximately -170m we will lower the graph so that Binary Slicer has something to distinguish. The output of the latter will be sent to a file through the File Sink block that is already familiar to us.
Note that such a scheme in practice is complicated by modules such as Rational Resampler and Throttle. The first allows you to reduce the signal sampling rate in order not to operate with redundant data in the future, the second essentially works the same way and is used to reduce the load on the processor in cases where it is not necessary to process the entire data stream without missing values (for example, it is enough to just output data on the screen, like ours). It is also worth noting that for frequency shift it is considered more correct to use the Frequency Xlating FIR Filter block, but for the sake of clarity, we use Multiply for this.
Rice. 3. Type of signal as amplitude versus time
On the Waterfall Plot screen at zero second you can see a useful signal. It is displayed on the Scope Plot as amplitude versus time.
Rice. 4. View of the working diagram for working with the signal
INTERPRETATION OF DATA OBTAINED
So, we received a file with a sequence of bytes reflecting the signal in binary form. 0x01 - one, 0x00 - zero. For reading, let's create a simple script in Python that will interpret a sequence of ones and zeros above a certain threshold as 1 or 0, and also separate various signals among themselves.
When presenting the received data in hexadecimal form, we obtain the following sequences:
2e23a99426bd8018 2e23a929426b805e 2e23a91f29428039 2e23a9031f298058 2e23a9cf031f809e Description: Today I want to tell you about one unique application that can warn you about a car theft. Yes yes, you heard right. There is an application that works like a car alarm. It's called from the developer HIPDRIVER.ME. You can download this signal from our website. The free version is limited to 2 hours of work (security time).
Application features: - displaying the movement of a car during theft or evacuation in your personal account; - displaying the location of the car, for example in a large parking lot; - beacon mode; - energy saving mode; - possibility of satellite tracking via GPS; - works wherever there is a GSM connection; - the ability to adjust the sensitivity of sensors both from the application and through your personal account; - timer for turning on the alarm; - and much more.
To view the functionality, I recommend going to the official website of the developer of this application. What pleased me very much was the clear and simple interface and the ability to work in 3 modes: 1) Telephone - telephone; 2) Dialing; 3) SMS.
In the first mode, an organization needs to have two phones under management operating system Android. In which one phone will act as an alarm system, and the second as a control panel. I want to say it’s very convenient, but in this case, as in others, you need to leave the phone in the car. Using sensors, the phone determines whether external conditions are changing or not. And as soon as the phone changes its position even a little, it will let its owner know that something wrong is happening. When using the 2nd method, the phone will start calling the phone number specified in the settings. With SMS it’s the same thing as with dialing. Using the application is very convenient and pleasant; all actions take a minimum of time. We can summarize. Conclusion: After testing the application called I was pleasantly surprised. I set the sensors to maximum sensitivity and tried to deflate two wheels, the alarm worked properly. I also checked the GPS, put the phone in my wife’s car and watched where she was going. I can say that everything works like clockwork. One thing, don’t forget that the phone needs to be recharged. Of course, this application will not replace a good and high-quality alarm system, but it is very suitable as an alternative. On a 5-point scale it deserves the maximum score. And remember, even the coolest car alarm cannot protect your car 100% from theft. Thank you for your attention.
Description: Application " Anti-theft alarm" will help prevent the theft of your device. The anti-theft alarm can be used to discourage family and friends who really like to spy when you are not using your tablet or phone. An alarm will sound if the device is moved or disconnected from the charger. The program is not bad to use to protect children from using the phone without permission. One of them. best apps to protect your device from burglars. Home screen: There are two main buttons on the screen:
Settings: In the settings of the Anti-Theft Alarm program, you can change the alarm signal, password, and theme. It is also possible to set a grace period before the alarm. In the Pro version you will have access to automatic start applications after rebooting your device, new design templates, battery protection. M a rich application that turns a smartphone into an “electronic watchman” - the idea, in general, lies on the surface! As is known, in good modern alarm system, in addition to the traditional reaction to body vibrations, breaking glass, opening doors, turning on the ignition, etc., it is possible to control it via a channel mobile communications, communicate with the owner through phone calls and SMS. And besides, do various useful things using GPS: report the coordinates of a parked car, when a car leaves the boundaries of a pre-designated area, draw a route track... Actually, most smartphones could do the same thing if they were controlled by an application with an operating algorithm close to the operating algorithm of a car alarm. There are many such applications, and although some of them are designed to counter the theft of the phone itself, some are also designed to protect the car. It's easy to find them in the Google Play app store. And outdated devices that have long been “decommissioned” are suitable for these tasks. “Alarm” applicationsLet's install and test a couple of programs to understand their essence and capabilities. The application, simply called “Signalka,” is free and has a fairly simple and logical interface, which is good news. It also has two operating modes.
In the application settings, you can adjust the sensitivity of the vibration sensor, the radius of the tracking zone, the exit of the car beyond which will trigger an alarm (from 20 to 120 meters), as well as the events for which SMS will be received - the activation of a motion sensor, turning on/off, low battery and etc. There is also a tracker mode, in which after the car leaves the tracking zone, the device will start sending you coordinates every 5 minutes.
 The author of another application, under another “original” title “ Security alarm”, designed its interface, frankly speaking, unsuccessfully. Not everything in it is intuitive, there are a lot of abstruse problems that burden the average user, such as a running graph of vibrations of the smartphone body. There is no intuitiveness - you need instructions for use. There are instructions, but among the on-screen sections (“Main”, “Calibrations”, “Settings”, “Other”) it is not visible - it is found only if you click on the three dots in the upper right corner of the screen, where an additional mini-menu is hidden. Moreover, the application is also paid... One way or another, it is curious that the developer in the program focused on the fullest use of the smartphone’s motion sensor – the accelerometer. The user can not only adjust its sensitivity according to the “more/less” principle, as in the previous program, but adjusts it in numerical values independently along each of the three coordinate axes X, Y and Z. In the application settings, the user can set the angles, the achievement of which will lead to to trigger an alarm and send an alarm SMS. And in the same SMS you will receive digital data about changes in nodes along the coordinate axes. If the position of the smartphone is known, it will probably even be possible to draw conclusions about what is happening with the car, recognizing jacking, sagging on an ice crunch under the wheel, or loading onto a tow truck. Whether it is convenient and how necessary it is is an open question, but in any case, this solution is unusual, distinguishing the application from others.  This is what messages that come from a smartphone as an alarm look like:  Benefit or pampering?An unpleasant feature of a telephone-based “alarm” is that it absolutely does not have any protective functions. It will be able to notify the owner of an alarm, but it will not be able to prevent thieves from starting the car if there are no other protective electronic or mechanical means on the car. Accordingly, the question arises: In what situations might a budget alarm system from an old cell phone make sense? Actually, there are two options here.
Installation and power supply of a smartphoneFinally, an important digression. The descriptions of “alarm” applications do not say anything about the power supply of the smartphone, and not everyone will immediately think about it. However, powering your smartphone, if you suddenly decide to use it as an “alarm”, is a special issue. With GPS and GSM turned on, as well as with the G-sensor constantly active and waiting for vibrations of the car body, the device will be discharged in a maximum of half a day. And if we use a “retired” old man or a new, but ultra-budget gadget, the battery of which is far from the records of capacity and quality, it’s good if the battery lasts for several hours... This means we’ll have to arrange it for the phone constant food. This is not a difficult task, but it requires some fiddling. First, you need to find a place for your smartphone in the car interior that is both invisible during a superficial inspection and relatively accessible so that you can perform some actions with the touch screen if necessary. Well, so that the GPS works. These are, to put it mildly, mutually exclusive things, but we hope you can handle it. After this, you will have to connect the power wire to the place where the smartphone will be hidden from a point where 12 volts are constantly present (regardless of the position of the ignition key). And then, in the immediate vicinity of the smartphone, from these 12 volts you need to make 5 volts - using car charging with a microUSB plug on the cord. It should be noted that constantly connecting the phone to charging is an acceptable, but not the most optimal solution... Yes, after the charging is completed, the battery controller goes into a seemingly safe standby compensation mode, but... Editor's Choice 
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