carsecuritycallbackcircuit - Cell Phone Call Alert Security System Circuit

Cell Phone Call Alert Security System Circuit

This circuit will give call back alerts in the form of blank calls on your cell phone whenever it senses a break in or intrusion inside the particular restricted area where it has been installed for the intended security monitoring.


The cell phone call alert security system circuit which needs to be installed incorporates a cheap cell phone as the modem which is actually used for triggering the warning calls in the owners cell phone.


The above modem cell phone is first attached with its own SIM card as normally done with any cell phone.


For setting up the cell phone, the cover is removed and a couple of wires are neatly connected with the pads which represent the "green" button or the calling button of the phone.

After securing the two connected wires with the green button terminals, the phone is again sealed back to it normal condition.

The external ends of the above wires are then connected to the relay contacts of the control circuit as shown in the figure.

Before the installation, a call is made from the above modem cell phone to the owners cell phone so that it gets recorded inside the green button as the "last call" made from the cell phone.

Now every time the green button is activated thrice, a call gets connected to the owners cell phone.

Since the wires from the call button are connected to a relay, it simply means that if the relay contacts gets energized thrice, would result a call being sent from the above cell phone.

How the Control Circuit Works

  1. The control circuit basically consists of a hold circuit and a pulse circuit.
  2. The "hold circuit section is made up of two NAND gates configured as a timer cum latch circuit. N1 and N2 together with C12 and R14 form a timer circuit, while the resistor R15 keeps the output latched as long as the timer counts and its timing lapses.
  3. After which the output reverts to its original position.
  4. The input of the above latch is connected to a reed relay sensor which may be appropriately centered for initiating the magnetic contacts when a possible intrusion takes place.
  5. The reed relay activates a relay (left side of the diagram) only momentarily via the capacitor C10.
  6. When the above relay contacts close, N1, N2 latch, and generate a negative or a logic low at the output.
  7. This logic low instantly grounds the reset pin of another timer IC 4060.
  8. This immediately prompts the IC 4060 to start counting.
  9. The process generates a set of three pulses at the pin #15 of the IC activating the relay thrice via the relay driver stage. This activates the cell phone modem which starts sending a blank call to the assigned number or the owners cell phone.
  10. Pin #2 makes sure that the IC counting and the output from pin#15 gets locked after the three relay pulses, this is done by sending a high pulse from pin #2 to pin #11 of the IC.
  11. The IC remains in this position for so long as N1 and N2 are in the counting mode after which the output of N2 goes high and the entire circuit is reverted to its original state and back in the alert mode.
  12. The modem cell phone is kept in a charged state by employing a 7805 charger circuit.

This circuit was exclusively designed and invented by "Swagatam".


carsecuritycallbackcircuit 1 - Cell Phone Call Alert Security System Circuit


All Resistors are ¼ watt 5% CFR, unless otherwise stated.
T2 = BC547
IC2 (N6,N7,N8)-4093
Relays-12V/400 Ohms


40 thoughts on “Cell Phone Call Alert Security System Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hello. I didn't understand the part when you take the wires from the cell phone. How do I know which wires and what should we do with them? Thank you for this project!

  3. hello . we are not able to connect the relay in the circuit , we have 5 pins in the relays , so which pin is related to the suitable connection , in your figure , there are 4 connections , and we have 5 pins in the relay ??? so please if you could help us to resolve this problem . thank you

  4. sorry for disturbing you , we are making a project and it's very urgent we need your help . we connected the element of your circuit , but we are facing some problems concerning the relays and the timer . the first relay is active but the second is inactive although there is 0V at pin 12 . and how can the pin 15 generate the signal in order to saturate the transistor . thanks for your response .

    • The circuit is very simple and perfect, I have tested it. Check all the connections properly there might be some mistake while assembling.
      The circuit should start working instantly if everything is done as per the diagram.

      Please note:
      C11 = 102/ disc
      R11 = 330K

  5. Mr Swagatam , i have a question : in the circuit below , threre are two NANDS , i didn't understand why you placed two NANDs and not one NAND. thank you

  6. Hello , is there a way to change the old cellphone you have used to an android phone with no hardware call button?

  7. Mr Swagatam , I have subsitute the relay coils to the transistors BC547B. But the circuit is always on when tested. Is it the transistor problem? Or you have any solution to it.

    • Appreciate your interest,
      But I am sorry I cannot help you with this particular product, as I am now interested in the sale of this product.


  8. Good day Sir,

    I know that your circuit was intended for sale,

    but i hope you could still grant a little help Sir,

    I was able to build your circuit since last week Sir

    my question is how could you able to reduced into 3 pulses since the inputs of the IC produces

    2,4,or 8 pulses only.

    Thank You Sir.

    • three pulses won't be possible with a 4060 IC, you can get either 4 or 8 or 2, meaning in multiples of 2…. you will have to design completely different circuit for it.

  9. hi sir, I have already started constructing my own version of this gsm based alarm ckt before I saw your website. but i'm still halfway there. I'm only using IC4020. Along the way, I accidentally made a monostable IC4020 ckt, after i mistakenly reversed voltage polarity and shorted certain pin outputs. i'm using this to lock-up the system (preset time is 2 minutes) while in dialling and calling mode, enough to make a successful call, maybe. My question is – can I utilize the dialing & calling mode of the mobile instead of using a preset timer ckt? I utilize the sound output of the mobile as a trigger to lock the system, so as not to receive any interruption from sensor if it has sense another intruder while the system is dialling, but the problem is if ever there's an incoming calls or txt message or auto text from mobile company, such will create a false pulse to lock the ckt.
    What signal to utilize that indicates the mobile is still in dialing & calling mode?
    any comment sir?
    thanks you

  10. hi sir, i found out that i can't finish my project using the speed dial because i don't know how to make an IC to produce longer signal enough to activate the speed dial feature of the cellphone. It's because if its relay will switch on the pad on a short pulse, the cellphone will not understand it as a command for speed dialing. Such will only be understood by the cellphone as encoding a single numeric character.
    In summary I need the circuit to also produce
    1. several short pulses (to reset the mobile to Home menu)
    2. then single long pulse ( longer than 4 seconds) to activate speed dialing a number. I understand IC4017 can produce this long pulse, but i don't know how to integrate it to the system, minimizing the use of relays.
    Kindly help me.

    Thank you

  11. Hi Swagatam,

    I want to use 4 x 1.5V batteries instead of a 12V source to make it portable. Problem is I don't think I can get a relay which will operate at such a low voltage. Can I substitute the speed dial relay for some kind of solid state device. I have noticed that touching the copper speed dial contacts with a finger is enough to activate the phone (high impedance/capacitance?)

  12. Hello Mr.Swagatam .Its a brilliant project.
    I had a small doubt.
    Where is the +ve terminal of diode D9 connected to? And also one of the terminals of the mobile phone? What actually is 'tone amp'?

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