Comparison Sheriff ZX-940 vs Sheriff APS-2500

Communication format of an alarm installed in a car with a key fob or other device used for control.

— One- way communication. With this type of connection, the user can only send commands from the key fob to the alarm system — opening and closing the car, turning off a triggered alarm, etc. Communication in the opposite direction through the key fob is not available, the sound and light signals of the car itself are responsible for the notification — a horn, a siren, flashing headlights, etc. Single-sided models are inexpensive and available, but are not well suited for situations where the car is out of sight / hearing — for example, when storing a car in a parking lot far from home or in a garage.

— Two -way communication. Models that allow communication in both directions — both the transmission of commands from the key fob to the alarm, and the sending of various notifications from the alarm to the key fob. In addition, this communication channel can be supplemented with a GSM module (see below). Anyway, two-way communication provides many advantages and additional features compared to one-way communication. For example, at a later time, you can turn off the siren so as not to disturb others, and at the same time, you are guaranteed to receive alarm signals; when the siren is turned on, duplicating the alarm signal on the key fob allows you to unambiguously determine what your car is...“screaming”; etc. The main disadvantage of bilateral models is the higher cost.

— Keyless. This category includes all models of car alarms that do not involve the use of key fobs at all. One of the most popular options in such devices is control from a mobile phone, via a GSM module; such communication is generally similar to two-way communication (see above), it is described in more detail in the paragraph “GSM-module”. In addition, labels can be used (see "Functions"), as well as buttons directly on the ignition key; the first option assumes one-way communication (also see above), and the second can work both in one and in both directions. The specific combination of these communication methods in different models is made different, and it is on this combination that the features of controlling the “signaling” largely depend.

The number of independent security zones provided in the alarm system.

Each independent zone has its own set of sensors — for example, one zone can cover the doors, the second — the boot, the third — the hood, etc. This, in particular, makes it possible to determine in which place an attempt was made to penetrate, a blow occurred, etc., and to give an appropriate signal — up to showing a specific place of operation on the display of the key fob with two-way communication (see "Type of communication"). In addition, separate activation / deactivation or a time difference can be provided for individual security zones. For example, upon auto-arming (see "Security and Protection"), the alarm for the doors can be activated immediately, and for the boot — for some time later, which will make it possible to calmly pick up things from there.

The simplest modern car alarms have 1 – 2 security zones, in advanced models this number can exceed a dozen (which, in particular, allows you to provide your own security zone for each individual door).

— Service mode (Valet). A special mode of operation in which all signals and warnings are turned off, however (in some models) the ability to control car locks through the alarm remains. This function is convenient when using the services of service stations, car washes and other services, when completely “legal” effects on the car can be perceived by the alarm system as signs of intrusion and cause false alarms. When the system is in Valet mode, the driver does not have to leave the control key fob to the service centre personnel, which minimizes the possibility of signal scanning.

— Management of a regular key fob. The ability to control alarm functions using a standard key or vehicle key fob.
Modern cars and other vehicles are equipped with more and more complex electronic systems, and to control these systems, a regular key or key fob is often used. The same key/trinket can be used to control the car alarm. Of course, the specific functionality of such models can be different, it's ok to clarify it separately. The same applies to the compatibility of the signaling with a specific key or key fob — different manufacturers may use different communication standards, and it will not hurt to clarify the support of this standard by the selected "signaling" separately.
The main advantages of this function are, first of all, that it reduces the number of key fobs used to control the functions of t...he car, and at the same time allows you to use all the "chips" of standard key fobs / keys that were originally provided by the manufacturer. In addition, branded key fobs and keys are purely subjectively liked by many drivers due to the presence of symbols of a particular car brand.

— Management of windows. Possibility to control the windows of the car through the car alarm. Thanks to this function, the driver can raise and lower the windows of the car remotely, from a key fob or other control device. This feature can be useful, for example, if the car is already closed, but the windows are not fully raised: instead of disarming the car and getting to the power window control buttons, you can simply give a command from the key fob.

— Management of the opening of the boot. The ability to control the opening of the boot of the car through a car alarm, from a key fob or other control device. This function, usually, allows you to open and close the boot without disarming the doors (and other areas of the car) and without entering the passenger compartment. This is more convenient, and sometimes even safer, than working with the boot in the usual way.

— Locking doors when driving. Possibility of automatic locking of car doors at the beginning of the movement. This feature reduces the risk of a car being seized by force when intruders get into the passenger compartment by simply opening unlocked doors — for example, while stopping at a traffic light. Of course, the central lock can be closed from the driver's seat and manually; however, you can forget about it, while automatic closing works without driver intervention.

— Panic mode. The presence of the "Panic" mode in the alarm system allows the driver to manually turn on the alarm — with a siren, light signals, engine blocking, etc. This feature can be useful if the driver sees suspicious people at his car — in order to frighten off potential hijackers — as well as in other situations when you need to draw the attention of others to the car. In addition, in the absence of the "Search for a car" function (see below), a short-term activation of the "Panic" mode can play its role.

— Function "Polite backlight". Alarms with the function of "polite lighting" are able to control the interior lighting, providing the driver and passengers with additional comfort. For example, when the doors are opened, the lighting can turn on, facilitating placement and orientation in the cabin, and when you start moving and close the doors with the ignition off, it can go out. Turning the light on and off is often done smoothly, avoiding abrupt transitions and making it easier for the eyes to get used to it.

— "Take me home" feature. With this function, the alarm can control the headlights so that they (when the engine is turned off) do not turn off immediately, but after some time after pressing the switch and closing the door. Thus, you can use car headlights to illuminate at night — for example, if you need to walk from the car to the entrance in a dark courtyard on uneven asphalt. The time for turning off the “seeing off” headlights is most often about half a minute — this, usually, is quite enough for the purposes described.

— Function "Search vehicle". This function consists in the fact that, at the command from the key fob, the alarm system gives several short signals (light or sound, and in silent security mode — only light), signaling the driver about the location of the car or motorcycle. This can be useful, for example, in a large parking lot of a hypermarket or an entertainment complex, where the vehicle can get lost among other cars, and searching for it “manually” (especially if you need to carry purchases or roll a cart at this time) can be quite tedious.

— Hands Free function (label). This function allows the driver to control the alarm without using the key fob. A special tag is responsible for managing the operating mode, which the driver needs to carry with him, and a sensor system that responds to the approach and distance of the tag. Thus, when a person with a tag moves away from the car at a certain distance, the alarm is automatically armed, and, having noticed the appearance of a tag within the range of the sensors, it is removed. This format of work allows the driver to keep his hands free and not be distracted by the key fob; in addition, communication between the system and the tag is minimal, making scanning nearly impossible.

— Autostart on the voltage of the onboard network. Possibility of using an alarm to automatically start the engine in case of a significant drop in battery voltage. This situation may arise, in particular, when the car is idle for a long time, especially in cold weather. A dead battery is not only fraught with problems when starting a car: car alarms are often powered from it, so when the charge is exhausted, the car can be left unguarded. To avoid this, this possibility is provided: having fixed a voltage drop close to critical, the alarm starts the engine for a while, recharging the battery from the auto generator and preventing the described troubles. It should be noted that the use of this function is associated with certain restrictions and precautions; for more details about them, see above, in the paragraph “Autostart by temperature”.

— Function "call the driver". This feature allows a person at or inside the car to signal a call to the driver's key fob. Note that the call button is most often installed in the cabin, based on passengers; however, an external location may also be provided, allowing the driver to be called even with the car closed. In the latter case, the installation location of the call sensor is usually marked with a sticker with the appropriate inscription, for example, “Knock three times to call the driver”; and the call method is chosen in such a way that the alarm system can clearly distinguish it from an attempted opening or accidental impact on the car. However, this feature is only found on models with two-way communication (see "Communication Type"). In this case, we are talking about a separate call signal, and not about a general alarm signal, which allows the driver to more accurately assess the situation (and saves his nerves). “Calling the driver” can come in handy, for example, in a situation where the passenger remaining in the car felt unwell, or if the car had to be put in such a way that it blocks the exit of other vehicles. In the latter case, conscientious drivers leave a note with a mobile phone number on the glass, but with this function, you can do without a note — the main thing is that the range of the key fob is enough.

— Bluetooth Smart. This function allows the user to use a smartphone with a special application as a key fob to access the car. At the same time, in accordance with the name, communication is carried out via Bluetooth, due to which such authentication works even in the absence of mobile communication (for example, in an underground garage). The convenience of such alarm control is obvious: you do not need to carry an additional item (keychain or tag) with you, and the probability of forgetting your smartphone somewhere is much lower than the probability of not taking the same keychain with you. At the same time, the probability of interception of the control signal, according to the manufacturers, is practically zero. And in some models, owner authentication and disarming can be carried out completely automatically when the smartphone approaches a certain distance. Other functions (such as transmission of diagnostic data) can also be implemented via Bluetooth Smart, depending on the model. The main disadvantage is that Bluetooth Smart alarms are very expensive. In addition, this technology is far from compatible with every smartphone, this point needs to be specified separately.

— Diagnostics of malfunctions. The ability to use alarms to diagnose various failures and malfunctions. In different models, the implementation and capabilities of this function may be different. Most often, this function involves at least self-diagnosis: the alarm “interrogates” the sensors with service signals and, if one of them fails, notifies the user about this. However, more extensive possibilities may also be provided — such as obtaining data from the car's own sensors (for example, about a decrease or complete disappearance of battery voltage). This not only allows you to monitor the technical condition of the car, but also provides additional security — for example, a decrease in the level of gasoline in the tank may be a sign that it is being drained.

Features for automatic start and shutdown of the engine, provided in the alarm. In some cases, using automation is much easier, more convenient, and even more reliable than starting and stopping the engine manually.

— Autostart by timer. Alarms with this function are able to automatically start the car engine at a certain time set by the driver. This feature allows, in particular, to provide additional comfort and save time on warming up: since the owner does not need to be in the car to start the engine, he can come later, get into an already warmed up car and drive right away.

— Autostart by temperature. The ability to use an alarm to automatically start the engine for warming up — in the event that its temperature drops below certain values. This function is intended for the cold season, when the machine has to stand outdoors for a long time (for example, all night). Starting a cold, and even more “frozen” engine is associated with a number of problems: the oil becomes thicker, and the battery can “sit down” and produce a weaker current than expected. To avoid such problems, some car alarms are equipped with an auto start function based on temperature: when the engine temperature drops below a certain level, the system automatically starts it to warm up. This ensures that the temperature is maintained sufficient for a comfortable start of the engine at any time. On the other hand, fuel...is spent on regular warming up of the engine, and in enclosed spaces and other places where exhaust gases are undesirable (and even dangerous), this function is poorly applicable. Thus, most alarms with this feature have limitations related to fuel economy — for example, starting less than a certain number of times during one idle time, or the maximum engine warm-up time.

— According to the voltage of the on-board network. Automatic start of the car engine in the event of a voltage drop on the on-board network (in fact, the car battery) to a certain level. By using this function, you can avoid a decrease in battery charge and related troubles — including not only starting “with a pusher” or “lighting up”, but also completely turning off the alarm (if it does not have an autonomous power supply). Of course, the operation of autorun requires additional fuel costs, but usually such alarms have a number of restrictions aimed at minimizing such costs. But when parking a car in a closed room, this function should be used with caution — it requires good ventilation, otherwise the periodic engine start will lead to the accumulation of exhaust gases.

— Turbo timer mode. Possibility of operation of the alarm as a shutdown timer for an engine equipped with a turbocharging system. During driving, the turbocharger can reach high temperatures, and the oil circulation necessary for effective cooling is ensured by the operation of the engine. If you immediately turn off the car after driving, the heated compressor will actually lose the main cooling system, which can lead to damage and even failure. Therefore, the rules for operating turbocharged engines prescribe, after stopping, to allow the engine to idle for a while to cool the turbocharging system. However, the driver does not always have time to wait for the compressor to cool down. The turbo timer "simplifies life" for drivers of turbocharged cars: it keeps the engine running for some time after the ignition key is removed, after which it automatically turns off the engine. This eliminates the need to wait without removing the key from the ignition and manually control the idling time.

— Webasto support. Car alarm support for Webasto equipment, more precisely, the proprietary W-bus protocol. Webasto is known primarily as a manufacturer of starting heaters for cars, however, in addition to this, the company produces many other components, mainly for “climatic” purposes — air conditioners, sunroofs, etc. Accordingly, Webasto support allows you to connect an alarm to equipment under the W-bus and control this equipment through it. Note that W-bus controllers are also available separately, but it is usually easier and more reliable to buy a compatible signaling right away. — Support of the signaling of the Start/Stop function. This function is mainly intended to give the driver the ability to start the engine without using a key, simply by pressing a special button. At the same time, some models are designed for installation in a car where such a button was originally provided, and we are only talking about compatibility with a keyless start system; others are equipped with their own button and can even be installed in cars that were initially started only with a key.
In addition, models with the "Start / Stop" function can have the function of remote engine start on command from the key fob. This can be useful, for example, to save time on warming up the car before driving in cold weather: you can start the engine without leaving your home, and then get into an already warm car.

— Automatic transmission support. Signaling compatibility with automatic transmissions.
Such systems are structurally more complex than traditional mechanical boxes, they are closely related to the electronics and controls of the car. Therefore, for the correct operation of the autorun functions on a car with automatic transmission, it is necessary that this type of transmission is initially supported by the alarm system. If the “signaling” covers only locks and other functions that are not actually related to the engine, this feature is not mandatory.

— Support for diesel engines. This feature is indicated for car alarms that have a specialized mode for starting diesel engines. One of the differences between such engines and gasoline engines is that they use the so-called. glow plugs. For normal operation of the diesel engine, it is necessary that such candles warm up to operating temperature; heating starts immediately when the ignition is switched on, but it takes time. These moments are taken into account in the "diesel" mode: the alarm first turns on the ignition, and gives the start command only after the candle warm-up indicator goes out.

The maximum distance at which the ability to control the alarm from the standard key fob remains. In other words, this is the greatest distance from which the driver can give the system a control signal. This parameter should be distinguished from the reception range (see below): due to their small size, transmitters in key fobs are made relatively low-power, and the control range from the key fob inevitably turns out to be less than the signal reception range on the key fob (if the latter is provided at all in this model).

When choosing by this parameter, note that the control range is indicated for perfect conditions — that is, line of sight with a minimum of interference. The actual “range” of the key fob will inevitably be less, especially in the face of an abundance of obstacles. At the same time, modern car alarms most often have quite impressive range indicators. Thus, a distance of less than 500 m is considered rather small in this sense; 500 – 750 m is the average value, 750 – 1000 m is above average, and in some models a range of more than 1 km is claimed.

The maximum range at which a regular key fob in a two-way system (see "Type of communication") can receive signals from the central signaling unit. In other words, this is the greatest distance at which the driver can receive notifications from the alarm in the car on the key fob.

When choosing according to this indicator, note that the control range is indicated for perfect conditions — that is, line of sight with a minimum of interference. The actual "range" of the system will inevitably be less, especially in the face of an abundance of obstacles. At the same time, the main signaling units can be equipped with fairly powerful transmitters that can effectively “reach” key fobs over long distances. Thus, the claimed receiving range usually turns out to be on average twice the control range (see above), and even in relatively simple models it can exceed 1 km.

The display is one of the most convenient ways to display various notifications; it can work with almost any kind of visual information that is relevant for modern car alarms. Simply put, the display can show both numbers (for example, data from the autorun timer, see "Functions"), and text (for example, the inscription "Call"), and graphic data (such as a car diagram showing the status of each zone protection). Thanks to this, key fobs with screens are well suited for even the most versatile and advanced alarm systems; However such versatility also affects the price.

Note that this feature is found only in models with a two-way type of communication (see above) — it simply does not make sense to equip a one-sided key fob with a display.

Availability of alarm protection from scanning ; if the characteristics specify the type of such protection, it is also given in this clause.

Scanning is used by attackers to intercept the control signal from the key fob; by forging such a signal, the hijacker can safely open the car. Accordingly, this protection is aimed at preventing such hacks. And its main types nowadays are dynamic code and dialog code, here are the features of each of these methods:

— Dynamic code. The general principle of dynamic coding is that each time you press the button to turn on or turn off the alarm, the key fob gives a new, unique signal. Most often, the Keelog algorithm is used for this; it assumes that the signal from the key fob contains data on the serial number of the device, the number of clicks and the secret code that the central unit also “knows” (this code is written at the factory and is unique for each alarm). Based on the serial number, the system performs general identification of the key fob, the click counter confirms that the signal has not been sent before, and the secret code acts as an encryption key. Thus, even if an attacker intercepts and copies the signal from the key fob, this signal will be outdated and, accordingly, useless; and it is impossible to decipher this signal and reproduce the desired version without a secret code.
The main advanta...ge of systems with dynamic coding is simplicity and, accordingly, low cost. However, this method in itself is less perfect than the dialog code, it provides a lower degree of protection against interception and hacking — with the help of the so-called dynamic code grabber with a jammer, an attacker can still intercept the control code under certain conditions and open the machine. However this procedure is quite complicated and does not give a guarantee; so in general, dynamic code is a good option for inexpensive cars that are not particularly attractive to professional crackers. But for maximum protection, it is still better to use dialogue systems.

— Dialogue code. Protection operating on the principle of “friend or foe” recognition: before giving a control signal, the key fob and the central unit exchange service data, identifying each other and making sure that the signal comes from the rightful owner. This is done in the following way. When you press a button on the key fob, it sends a connection request with data about its serial number. The central unit checks the serial number and, if the result of the check is positive, sends a randomly generated number to the key fob. The keyfob processes this number according to a certain algorithm and sends the result (together with a request for action) to the central unit, which performs calculations according to the same algorithm; if the results agree, the defense gives the go-ahead to execute the command. The algorithm used for calculations is unique in each individual signaling, and so-called hash algorithms are used to encrypt the transmitted data. Due to this, the dialogue code is almost impossible to crack: for this, the attacker must intercept 3 data packets (request, riddle, guess) and decrypt 2 of them, while without knowing the key (embedded in the alarm itself and inaccessible without physical access to the device), such a decryption nowadays is inaccessible even to the most powerful computers.
Dialogue systems are naturally somewhat more expensive than dynamic ones, but this is more than offset by a high degree of security.

This function is completely similar to the vibration signal used in modern mobile phones. Its purpose is to give signals in conditions in which sound notifications are undesirable or ineffective. As an example of such conditions, in particular, lectures and other events where it is supposed to turn off the sound, or noisy environments (concert halls, clubs, etc.), where the vibration of the key fob in your pocket is felt better than the squeak of its dynamics, can be cited.