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Cell Phone Call Alert Security Circuit

Cell Phone Call Alert Security 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".


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



About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

18 thoughts on “Cell Phone Call Alert Security Circuit”

  1. 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?)

    • Hi John, it can be probably done by using bidirectional electronic switch such as in IC 4066….any other method is not recommended

  2. i want this project for final year with if anyone open my door then i receive a call or sms or alarm on my cell from system send me cost

  3. 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

  4. 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.

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