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Cell Phone Controlled Door Lock Circuit

Cell Phone Controlled Door Lock Circuit

Controlling your door lock through your personal cell phone was never this easy. Learn how to build a simple electronic circuit that will help in converting your ordinary door lock into a high security door lock which can be now controlled through your own cell phone.

Your ordinary door lock can be now very easily converted into a cell phone controlled high security door lock. Learn the entire building procedure through some simple instructions and circuit schematics.


A very simple configuration using a low cost cell phone (used as a modem) and an electronic circuit can be build to control remotely a high security door lock. Once the unit is built and attached to a door, by simply assigning your personal cell phone’s number inside the modem cell phone, you can alternately lock and unlock a particular door by sending subsequent “miss calls” through your cell phone to it from any part of the world. We use a NOKIA 1202 as the modem cell phone here for the project. Let’s proceed and learn the simple instructions required to complete the project.

Cell phone controlled door lock circuit through missed calls

How the Circuit Functions?

The basic concept of the project is to detect a particular ringtone from a SIM supporting modem and use it to toggle the electronic circuit and the load (door lock) correspondingly.

The very specific and unique ringtone – “Beep Once” or the “No Tone” is available with every NOKIA cell phone. And also this ring can be assigned to any particular fed number of the cell phone.

So this ringtone becomes specific only to that particular number and will be sounded every time a call is received from the assigned number.

This facility has been ideally exploited here. A 5 volt regulated supply is used to trickle charge the modem round the clock so that its battery is never discharged. This supply also goes to the IC 4093 = pin 14 (+) and pin 7(-). An in-built cut-off system inside every NOKIA cell phone ensures a safe charging.

The circuit functioning may be easily understood with the following explanation.

The FIGURE above shows a simple three transistor amplifier circuit which is basically used as a tone amplifier.

On receiving a “miss call” from the assigned number (owner’s cell phone), the modem immediately responds and produces the desired ringtone (“Beep Once”).

This tone frequency is collected from the modem’s headphone socket and applied to the tone amplifier’s input. The ringtone is suitably amplified and is used to toggle a relay momentarily.

This relay connects a 5 volt trigger pulse to the input of CMOS flip flop circuit and also sounds a buzzer.

The flip flop toggles in response to the above action and activates the following transistor/relay locking mechanism.

A car central lock has been effectively integrated with an ordinary manual locking shaft to form an excellent door dead bolt. The whole system activates in a push pull manner to alternately lock and unlock the door in response to every subsequent “miss call” from the owner’s cell phone.

Parts List for the proposed cell phone controlled door lock circuit








R8= 180 Ohms

R9 = 1K




R13=10 Ohm




C8 = 0.1uF/100V



Transistors are BC547 and PNP is BC557



All Relays=12V/400 OhmDiodes
D5- D8=1N5408

Rest all Diodes are 1n4148


Construction Clues and Modem Cell Phone Configuration

Constructing the control circuit is very easy and may be done by just assembling the procured electronic components over a general purpose board by soldering. All the connections should be accurately done with the help of the given circuit schematic. Once the assembly is completed, it’s time to configure the modem cell phone.

The attached modem cell phone needs to be set up through the following steps:

Go to settings and select set the default ringtone as EMPTY. It means now at this position the modem does not produce any ringtone to any incoming calls. Also, switch off the message tone, keypad tone, start up tone etc.

Now feed your personal cell phone numbers (single or many as desired) through which the modem and the lock need to be operated.

Assign the required “beep once” ringtone to all these numbers.

The modem is all set. Integrate it to the control circuit through its headphone socket pin assembly. Also, connect the charging voltage input to it as shown in the diagram.

Your high security door lock is fully ready and can be installed over the door which is to be controlled and will lock and unlock it faithfully on receiving the subsequent “miss calls” from the assigned numbers.


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!

49 thoughts on “Cell Phone Controlled Door Lock Circuit”

  1. Hello sir I am leaving in a rural area where there is lack of mobile network. I request if possible to give a circuit to enhance mobile signal. Thank you for your guidance.

  2. I made with 2phones and i can tell 100% the gate is open or closed ,it worked but I had not implemented 6 months ago as I have to work smart on gate,battery,DC motor and many small things

  3. Hi,majum hope u r fine and happy,I suggest that u add a timer to the above circuit that it can close and lock after 5 minutes as it would not b left open accidently
    and for the modem tell the readers to open the phone and connect the input from the phone speaker

    • Hi Venni, it's the terminals which are closed by the ignition switch while the vehicle is started (button start)

    • you can go to any car spare part dealer and ask for the cheapest central lock actuator, you should be able to get one easily within Rs 200/-

  4. thank you sir.. i made this circuit for my final year project .. also got nokia 1280. will check if it works with solenoid .

  5. Hello sir. Can I use a solenoid instead of central lock for this circuit? How much vol o/p, will I get at the the central lock??

    • hello sanket, solenoid without spring tension may work, you can try it.

      the voltage will be equal to the supply voltage but will be activated only for a second or two

    • Hello Urvashi, presently I do not have the assembled kites with me.
      but first you must have access to a NOKIA1280 cellphone, which could be difficult to find today.

  6. Hi Swagatam,

    What kind of cellphone is compatible with this design? is there any particular model do i need to use?

  7. Hello majum how r u doing,browsing for cell phone ring access circuit i came across here ,earlier i had disussed u on other ckts ,,here i beleive that using 2 receiving ends means 2 phones can perfectly predict what is going remotely ON or OFF, if u like my opinion pls try to update the circuit,thanks for ur helpful nature and god bless u

    • Hello Jeelani, thanks for the suggestion but I am sorry I could not understand how two phones could solve the "call received" acknowledgement issue? may be you can throw more light on your suggestion.

  8. hello sir,i want to asked you how to make the cellphone call owner when the lock are disturbed and when the owner call back the cellphone it shut off the car system.
    Can i use the same circuit and what things must i add to make it happen.
    thank you…

  9. Mr awagatam

    I am kirankumar surati and going to make a circuit as you stated but i have some problem because i searched L1(piezo buzzer coil ) in market but can't buy it. when i say to seller that i need piezo buzzer coil in response they say there is not materials like this.piezo buzzer has only a plat.
    So please explain me how to find it or make ourselves.

    • Mr Kiran you can show them the followingomage:


      you may also build it at home by winding 32 SWG wire on any ferrite core, about 1000 turns.

  10. hi i am doing this project as my science fair project can you give any suggestion to me please
    thanking you,
    Vikas md

    • make the upper transistor stage first (T3, T4, T5) if you succeed with it, only then proceed with the flip flop stage and the central lock stage.

  11. hi mr swagatam sir can i ask where exactly the pin 14 of the ic1 is connected..can i connect it in any positive port or there is an specific port to connect it?and c3-c4-c5-c9- and c10 are non polarized capacitor right?so what is the exact value of those capacitor sir?thank you in advance

  12. hi Mr Swagatam
    my central lock motor draws 5 amps at start up, what minimum rating does the transformer need to have, is a 1 ampere transformer good, what if i replaced the capacitor by a battery, what characteristics dies the battery need to have (its permanently charging via the transformer).

    • Hi Aladin,

      You can use a 5amp transformer with a bridge/6800uF/50V filter capacitor network, this should handle the instantaneous current of the motor.

    • Hello Zaib,

      I am sorry to say that presently I am not manufacturing this unit due to lack of time, so this offer is discontinued now.
      You can try it yourself though, it's a perfectly tested designed.

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