Two options for burglar alarm with cell phone

Two options for burglar alarm with cell phone

The problem of protecting property has always been and will always be topical. This problem is especially urgent at the present time. That is why the profession of security guards is in such demand now, and in radio sources are constantly published descriptions of security systems. We present two variants of a simple and easy-to-use security alarm system that uses a cellular phone to transmit the alarm.

Option 1

The alarm system consists of a cellular phone and a control unit (Fig.1).


The control unit consists of three standby multivibrators (single vibrator) implemented on the DD1.1, DD1.2, DD1.3, DD1.4 and DD2.1, DD2.2 elements, an oscillating multivibrator on the DD2.3 and DD2.4 elements, two electronic switches VT1, VT2 and a reed relay K1.

The alarm works as follows. When the contact closure of the switch SB1 waiting multivibrators on elements DD1.1, DD1.2 and DD1.3, DD1.4 switch to unstable state. On the output of DD1.3 appears a high voltage (+6 V), which opens the electronic switch VT2, and the supply voltage is applied to the cell phone.

On the cell phone the ON (power on) button is locked in the pressed state, so when the power is connected the phone immediately turns on and starts to register to the network. After about 6s the single-oscillator DD1.1, DD1.2 switches to the initial state, the negative voltage drop from the output DD1.1 goes to pin 12 of DD2.1 and switches the single-oscillator DD2.1, DD2.2 to the unstable state. A high level voltage from pin 11 of DD2.1 goes to the enable input of the auto oscillator (pin 2 of DD2.3) and starts it up.

The multivibrator DD2.3, DD2.4 generates two pulses of 0.5s duration, which from pin 4 of DD2.4 are fed to the gate of transistor VT1 and open it. Electromagnetic relay K1 twice triggered and the contacts K1.1 and K1.2 closes the contacts OK button cell phone. Contacts K1.1 and K1.2 relay connected in parallel contacts OK button cell phone.

The phone makes a call to the phone number that is recorded last in the memory of outgoing calls. Then the single-oscillator DD2.1, DD2.2 is switched to its original state, the control input of the flicker DD2.3, DD2.4 is low voltage, and the flicker DD2.3, DD2.4 is off.

After about 100 seconds after the alarm is triggered the flicker switch DD1.3, DD1.4 is reset, the key VT2 closes and the cell phone is switched off. When you close the switch contacts SB1 again, the above cycle of the device will repeat.

The capacitor C5 provides filtration of the supply voltage of the cell phone. The length of the wires between the phone and C5 should not be more than 15 cm. Resistor R8 ensures the discharge of capacitor C8. On its resistance depends the time of readiness of the alarm system to actuate again when the contacts SB1 are closed.

When replacing the parts of the electronic part of the device it is necessary to pay attention to the leakage currents of electrolytic capacitors and switches VT1, VT2, because the economy of the device depends on it. In the standby mode the alarm system (together with the cell phone) consumes a current of about 0,5 μA, so the lifetime of the power supply (battery or battery of galvanic cells) is determined by the self-discharge time. In addition, the transistor VT2 must be able to withstand the high charging current of the capacitor C5.

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Made from serviceable parts the alarm requires a little tuning. Pressing the OK button of the cell phone should take place immediately after the message “searching for the network” appears on the phone screen. This moment can be adjusted by changing the unstable time of the single-oscillator DD1.1, DD1.2 (by selecting R2 or C1).

This time in Fig. 2 is 6 s.


The duration of the unstable state of single-oscillator DD2.1, DD2.2 should be 1,5 times as long as the period of oscillation of multivibrator DD2.3, DD2.4 (in Fig. 2 it is 1,5s.). It is regulated by changing the resistance R5 or the capacitance CZ. The oscillation quadrature of the multivibrator DD2.3, DD2.4 should be approximately 2.

If this is not achieved, then instead of R11 it is necessary to switch on the circuit shown in Fig. 3, and use the variable resistor R11 (Fig. 3) to set the duty cycle to 2.


The time constant of the time-retaining circuits R2C1, R5C3, R11C9 should be stable enough, so it is desirable to use tantalum or semiconductor electrolytic capacitors as capacitors C1, C3, C9.

Instead of a reed relay you can use an optocoupler, but then a limiting resistor must be included in the drain circuit of VT1. An ordinary electromagnetic relay can also be used, which operates reliably at about 4V. For example, you can use a common relay RES-9 (datasheet PC4524 200), having previously done some of the following modifications:

  • 1. The RPS-9 relay contains two windings connected in series. These windings should be connected in parallel. This will reduce the relay resistance by 4 times and, all other things being equal, reduce the relay operation voltage by 4 times.
  • 2. 2. Loosen the screw fixing the insulating block in which the moving contacts are fixed by several turns. In addition, remove the thick wire which connects the movable contacts (insulating block) with the relay’s external leads. In its place a thin stranded wire should be soldered. As a result, the force required to switch the contacts will be significantly reduced. This force can be adjusted by means of the screw fixing the insulating block.
  • 3. All relay contacts should be stripped and tinned with a mild lead solder (e.g. G10C-60). After that you need to wash the contacts with alcohol to remove the rosin residue. The air is now heavily contaminated and the silver contacts are covered with a black silver sulfide deposit even when the relay is closed. The solder-coated contacts provide a good contact and do not oxidize for a long time. In addition, the relay contacts can be treated with modern contact protectors (e.g. KONTAKT 61).

After completing the above modifications, the RPP-9 relay will reliably operate at 4V.

The supply voltage of the alarm system is selected equal to the supply voltage of a cell phone, i.e. 6 V. The supply voltage can be increased e.g. up to 12 V and a voltage regulator can be added between the capacitor C5 (Fig.1) and the cell phone.

Variant 2

The design of the above mentioned device can be improved, for example, by applying additional acoustic sensors. Such an improved alarm device is convenient to use in a car. The scheme of such alarm system is shown in Fig. 4.

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Because the alarm system is designed to protect the car, it is powered by 12 V.

As an acoustic sensor is used phone BA1, which is rigidly mounted on the body of the protected object. When noise occurs in the body of the car at the output of the sensor BAA1 is a variable voltage sound frequency, which is amplified amplifier made on the chip DA2, then through the potentiometer R 15 is fed to the input of the amplitude detector made on the transistor VT3.

When a strong enough signal transistor VT3 opens, and the voltage on its collector decreases, which leads to a decrease in voltage at pin 12 of element DD1.3 and trigger the alarm. This turns on the power amplifier, made on the transistor VT4, and the amplified sound signal from the phone BA2 is fed to the microphone of a cell phone (phone BA2 is located next to the microphone of the cell phone).

This high-level voltage from the output of element DD2.4 through resistor R17 and diode VD2 is fed to the base of transistor VT3 and puts it in a saturated mode. As a result the alarm system will not respond to the acoustic sensor signals for some time. This is necessary so that there will be no blocking of the alarm system when it is on because of the acoustic coupling between the telephones BA1 and BA2.

The potentiometer R15 is used to adjust the sensitivity of the alarm. The elements R14C11 form a low-pass filter. The elements R19 and VD3 protect the emitter junction of transistor VT4 from reverse voltage breakdown. The diode VD1 protects the circuit in case of wrong polarity of the power supply. The electromagnetic relay is replaced by two optocouplers VS1 and VS2 to increase the reliability of the alarm.

During operation, the cellular phone emits pulse signals, which can interfere with the operation of the low frequency amplifier. Therefore, it is desirable to shield the acoustic sensor and low-frequency amplifier, and to include low-pass filters consisting of chokes and pass-through capacitors in the wires connecting the phone to the alarm system.

At the same time, these wires can be lengthened to increase the distance between the cellular phone and the control unit. To suppress the internal noise of the low frequency amplifier an additional low pass filter can be inserted between its output and the potentiometer. The K157УЛ1А chip has a low noise level, so an additional filter may be needed only in those cases, when you need a very high sensitivity of the acoustic sensor.

In principle, you can exclude the power amplifier and the phone BA2 from the circuit and use a cell phone microphone as an acoustic sensor. To do this, you need to rigidly fasten the body of the cell phone on the body of the protected object and ensure that the phone is able to emit radio waves. For example, in a car you can use brackets to tightly press the cell phone to the side window of the passenger compartment. At the same brackets should be made of insulating materials (wood, plastic, etc.).

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GSM security alarm systems: the best models and peculiarities of choice

The security of your own home, whether it is an apartment or a country house, is in the first place for any homeowner. GSM home alarm system will be able to notify the owner about the problems in time. And in some cases, it can even mitigate the consequences of violations.

What is it and how is the system set up?

The GSM security alarm system is a protective system that transmits information to the owner of the house or apartment about the intrusion of intruders. The signal is immediately received via cellular communication, allowing the owner to react quickly and take the necessary steps to remedy the situation. Alarm system will also be able to quickly notify about disturbances in electricity, heating, smoke, gas leakage or shutdown, water leakage.

Modern technology allows you to turn on and off devices from a distance. For example, if the temperature in the apartment starts to fall rapidly, you can switch on the heater with the help of an alarm. But you can also cheat and show that there is someone in the house. To do this, you need to remotely turn on the light, and this can scare away potential burglars.

Such features are only available in high-tech models, which are not cheap. However, the result of their work surpasses all expectations.

The principle of the alarm is based on the ability of the sensors installed in the room to read any change. Once the change has been detected, it is transmitted to the control device. Then there is an analysis of the received data. The information is transmitted to the owner in the form of a message on the phone. Data is transmitted via the GSM module. It should be noted the format of messages, that is, it can be:

  • voice message;
  • written text;
  • MMS;
  • GPRS.

The usual alarm set includes the following devices:

  • control unit with built-in GSM module;
  • fixing sensors;
  • External GSM antenna;
  • signal devices such as sirens, floodlights;
  • an additional power supply device, such as a battery or accumulator;
  • wires.

Depending on the purpose, you can choose the right equipment. For example, if, in addition to the sensors, you need constant video surveillance, you can install a camera.

Budget variant can be represented by a design with an autonomous power source. Inside the device is a module for alerting the owner, sensors to track sounds and movements. Such a system is able not only to transmit messages, but also to turn on the siren, light. Sensors should be placed in places where there is the greatest likelihood of intrusion or other violations. There are the following types of sensors that record:

  • breaking glass;
  • touching a door or window;
  • movement;
  • gas leakage;
  • smoke;
  • increase in temperature;
  • destruction of the wall.

Advantages and disadvantages

GSM alarm system has its pros and cons. Among the positives are:

  • the possibility of video recording, the inclusion of light and sound signals;
  • rapid notification of the violation;
  • there is a possibility of online control;
  • no special staff to manage the system;
  • round-the-clock control of the house or apartment;
  • there is a possibility to control switching on and off some home appliances;
  • availability of different types of messages;
  • wireless alarm system is characterized by ease of installation, configuration;
  • the possibility of connecting additional equipment to expand the ability to monitor the situation inside the premises;
  • it is possible to connect several numbers for notification.
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There are also negative aspects:

  • the message to the phone can be received only when in the cellular network access area;
  • there is a possibility of blocking the alarm signal by intruders with special equipment;
  • installation of a wired system requires certain skills, it is better to install such an alarm system at the stage of construction or renovation;
  • There is a possibility of signal violations in case of damage to the wires.

Best models

Alarm systems come in several varieties.


The main difference between this system is that the connection between devices is carried out with the help of wires. When a dangerous situation occurs, the sensors record changes and transmit a message to the owner of the dwelling. Such models are best used in small rooms.


Communication between devices is carried out thanks to a radio signal. There is no connection to the general electrical network. With the help of a sensor, changes in the house are recorded. The information is transmitted to the owner in the form of a message on the phone. Suitable for use in large private houses, cottages. The components of some devices can be located at a distance of up to 40-50 meters from each other.

It is important to note that there are combined models, which have the ability to connect wired and wireless sensors. This provides greater reliability of the system functioning. To ensure the best control of the situation, it is recommended to choose models with a camera.

A number of models can be included in the rating of popular systems.

Sapsan .

The device provides protection against intrusion, as well as fire safety in the house or apartment. The package includes a GSM module, wired and wireless sensors, a device with notification to the phone. Control takes place via mobile communication. With a temperature sensor can record changes in the home and make the necessary adjustments. You can connect up to 10 numbers for alerts. Thanks to the availability of a backup power supply, the alarm system can function in standalone mode for up to 12 hours.


The device is suitable for use in residential, commercial premises, small garages. In the event of a dangerous situation, a siren is triggered. The system allows you to control the situation in the room from a distance using a cell phone. It is possible to install wired and wireless sensors with different functionality. Characterized by ease of installation and configuration.

Strazh Universal

Alarm system can control the situation in a residential or commercial premises. It is suitable for large and small areas. Such a system includes the possibility of installing a listening device, external GSM antenna, control from a cell phone.

The system provides alarm notification via Internet. It does not require a lot of traffic. In the absence of a network signal is transmitted via GSM-channel to a cell phone. The device can be combined with a rotary standalone video camera. With this CCTV, you can view all the zones.

Falcon Eye

The equipment is suitable for protection of the house, apartment or small room, such as a garage. You can connect up to 32 wireless sensors to the system. Simultaneously with the transmission of alarm messages includes a siren. There is a possibility of sound recording.

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Alarm system is suitable for small buildings, garages. It is possible to connect additional devices that expand functionality. Autonomous operation is about 6 months.

Tips for choice

When choosing a security system, it is necessary to consider the purposes and conditions of use. If the device is chosen for a small room, such as a boiler room or a garage, you can choose a standard set of compact size. It is more reasonable to choose a wired version of the alarm system. When the equipment is purchased for a house or apartment, it is recommended to choose kits with the presence of a camera, the possibility of recording sound and installing additional sensors.

A cheap system is unlikely to provide a wide range of room protection. In this case, wireless and wired version of the design can be suitable. It all depends on the area of the home, as well as the possibility of installation.

When choosing, it is important to pay attention to the signal strength, the availability and speed of information transfer, the sensors’ response to changes.

And you should also consider the material from which the body of the control device is made. The reputation of the manufacturer is also important. Giving preference to systems of Russian or foreign production, it is necessary to carefully study the operating instructions and conditions of use.

Features of installation and setup

The set of equipment is accompanied by an installation manual. If you have some skills, it will not be difficult to perform the work. However, in order to get a reliable result, because it is about safety, it is recommended to contact professionals. They will help not only to install, but also to set up the equipment. Experts recommend buying ready-made kits, which are easier to install. However, this is not always suitable for owners who are anxious about the safety of their homes.

Conventionally, the stages of work include the following:

  • before installation, a study of the area is made, highlighting vulnerable areas;
  • numbers are fixed in the control device for informing;
  • a controlling device is installed;
  • sensors are installed;
  • a siren, a light, and a camera are installed.

After the work is done, the installation is checked for correct operation.

It should be noted that in order to ensure reliable security sensors must be installed on the door and windows. Indicators of window breakage, smoke and movement should be in every room. At the same time, it is necessary to comply with the standards of their installation. For example, movement sensors in a wireless alarm system should be installed at a height of 2-2.5 meters. The rules of installation are necessarily prescribed in the instructions. When installing a conventional alarm system with a minimum set of indicators, it is necessary to put a door lock.

Specialists also recommend installing double control on a single zone. This is especially true for vulnerable areas such as doors and windows. Dual control should be carried out by indicators of different types.

See the following video on how to properly install and configure GSM security alarms.

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