The project is about a home security system in which a cell phone is used as a device that will alert the owner of the house when an intruder enters the house.

## Step 1: About the Instructable

The owner just have to turn on the system before leaving his house.When an intruder enters the house in the absence of the owner the owner receives a call from a registered number which is the phone number of the hacked mobile phone at his/her house.

## Step 2: How Does the Circuit Work?

Cell phones have switches which when pressed short the terminals (gold plated) hence a number is seen on the screen

so what i have done is put my cell phone number on speed dial on the phone i hacked and when this number is pressed for a while i get a call.

so basically what we r doing is a circuit that will short the phone terminals. when a intruder enters the house.

IC LM358 is a dual op amp.

The output of an op amp is difference of the input times the gain of the op amp. ie. it compares the 2 inputs.

NOTE: refer datasheet for more details about the IC.

pin 2 of IC 358 is threshold a potentiometer is connected to it so it forms a voltage divider and a particular voltage is set up at pin 2 which the op amp compares with voltage at pin 3.

to pin 3 an LDR is connected it behaves in following way.

1) when light shines on LDR its resistance decreases hence a more positive voltage is set up at pin 3 which forces the output to be high.hence there is a potential difference at the terminals of the number on the cell phone.

2)when the light is cut off by the door which is opened by the intruder the LDR resistance increases hence a more negative voltage is set up at pin 3 which forces output to be low (0v).

in the equivalent op amp circuit shown Avid is approximately 0v when output is low and resistance Ro is very small hence the output is shorted to the ground thus shorting the 2 terminals of the cell phone.

## Step 3: Materials (electronic Components) Required

1) A Cellphone having press buttons (i used an old one which i had).

2) A 10K ohm resistor.

3) A 10K ohm potentiometer.

4) An LDR (Light Dependent Resistor) 10K ohm or A 2 legged IR sensor (IR sensors are better bcoz they are not affected by surrounding light).

5) An LM358 (Dual op-Amp) IC.

6) An Optical LASER (I used a red LASER). In case you are using IR sensors use an IR LASER.

7) wires.

## Step 4: Step 1:Hacking the Cell Phone.

The cell phone i used is an old nokia phone.

Remove the battery then remove the front cover then the keypad an then the transparent cover over the keys.

You will see a thin white film on the key terminals dont worry just remove this film using forceps but remember only cut the film on a single key from 0 to 9. I just pulled it out in excitement and now i have problems starting the device i have to manually start it by shorting the terminals using any metallic object.

## Step 5: Step 2: Checking the Polarities

Insert the battery back into the cell phone and turn it on.

I wanted to use key 3 for the speed dial so i was checking the terminals on key 3.

Put a multimeter on dc voltage measurement then touch the probes to the 2 terminals on the key then reverse the probes on the key terminals either way the multimeter will show a reading but it will show +ve DC voltage when the probes are on correct -ve ,+ve terminals.

In my case the inner one was positive and the outer one negative.

Solder a red wire to the +ve terminal and a black wire to the -ve terminal.

## Step 6: Step 3: Soldering the Circuit.

According to the circuit diagram solder the circuit.a small dotted board is enough as there are hardly any components.

NOTE: the circuit remains same if a 2 legged IR sensor is used.

Solder the red wire from the cell phone key to the output of the op-amp IC ie. at pin 1 and the black wire to the ground.

Solder the LDR to a small piece of board and solder wires to it (LDR does not have polarity so it can be connected any way to the main board).

## Step 7: Step 4:The Power Supply.

Use a cell phone charger just cut the jack and solder 2 wires to it which will be connected to the main circuit board.

The red one is +ve (Vcc on circuit diagram).

and black one is -ve (Ground on circuit diagram).

## Step 8: Step 5: Placing the Circuit.

Place the sensor and LASER on opposite sides of a door.

focus the LASER on the Sensor such that LASER falls on the sensor when door is closed and it is cut off from the sensor when door is open.

Insert any active sim card into the cell phone and register its number on your cell phone as 'security' or anything you like.insert the battery and turn the cell phone on.

turn on the power supply to the circuit.

## Step 9: Step 6: Calibrating the Circuit

Check video

We had kept a 10K ohm potentiometer for the circuit which will set the threshold for the op-amp.

Turn the potentiometer in either direction and check for a point at which

1)LED lights when door is closed and

2) it turns off when door is closed.

if you have reached the threshold point now don't change it.

set your phone number as speed dial on the key you have selected on the hacked phone.

press the home (call end) button to clear the screen.

The project is done.

now you just have to turn it on when you r going out.

## Step 10: Step 7:Extending the Circuit

Any intruder will never come through a given door so every door in the house needs this circuit.

the main boards will increase the times you have doors and the output of each and every op amp should be AND'ed (connected to inputs of AND gate (Digital IC 7408) and the final output should be connected to the mobile +ve terminal so only 1 cell phone is required.

## Step 11: Step 8: the Final Product

There you have it.

Do vote if u've liked my instructable and happy hacking.

<p>Hi there,</p><p>This is an interesting project. May I suggest something simple?</p><p>If you solder a reed switch (as suggested by <a href="https://www.instructables.com/member/rfitzgerald" rel="nofollow">rfitzgerald</a>) directly to the speed dial button, will it work? You will avoid building all the circuit you have shown here.</p><p>Thanks!</p>
Can I use a magnetic switch instead of the sensor?
ya you can
finally i made it...simple circuit ..great job
does it need a charger supply as input..? can we use a 9v battery?
Thank u...it really working . I am a beginner in electronic... and i made it for my room
<p>good job ,is there other other projects for old mobiles .</p>
<p>I need to make something like this but i lack the materials....would i use my radio?</p>
<p>How long does it require to make the call?</p><p>Because if an intruder gets into our home he'll not stay in one place and I think that it will keep on pressing the key every time the circuit is broken.(If we use mirrors to extend the laser ray) Plz tell the sollution!</p>
you can use mirrors to extend the ray. Make it like a network as seen in movies for top class security systems. it takes approx 5 to 10 secs to place a call. And intruder might not have knowledge of what hides behind the door so might not check.
<p>Is it really working . I am a beginner and i am doing it for a school project...</p>
<p>Great idea and instructable</p>
Thanks
<p>Hi .. I am doing the same but my output level used to be something like 1.67 v so it does produce a short. i am using lm 741.. please help</p>
Refer data sheet of IC 741.<br>Use the null compensation network.<br>U just need another pot to make the value 0.
<p>this project works perfectly,i just finished making it last night now am making additional projects like motion and sound sensor circuit. </p>
Awesome?
<p> but how to connect the charger and where</p>
The charger I've used is a power supply to the circuit.<br>And not the Mobile.
Hi<br><br>May I suggest that you establish workshops. You can do the train the trainer workshop.
Oh it would be my pleasure..
Hi<br><br>I need a system that connects on 2 windows and two doors. This is for business purposes. We are looking at a clientele of 500 house holds for the 1st quoter of 2015
Hi<br><br>sorry for the late reply.<br>The system can support n Number of doors and windows.<br>Just little extra electronics required.
<p>do you realy need an old phone to do that...</p>
Unless u hav a ton of money to spend
<p>is it really working??????????????????????????????????????????????????????</p>
Yes it works
Hi<br><br>I need a system that connects on 2 windows and two doors. This is for business purposes. We are looking at a clientele of 500 house holds for the 1st quoter of 2015
Hi<br><br>I need a system that connects on 2 windows and two doors. This is for business purposes. We are looking at a clientele of 500 house holds for the 1st quoter of 2015
Hi<br><br>I need a system that connects on 2 windows and two doors. This is for business purposes. We are looking at a clientele of 500 house holds for the 1st quoter of 2015
Hi<br><br>I need a system that connects on 2 windows and two doors. This is for business purposes. We are looking at a clientele of 500 house holds for the 1st quoter of 2015
<p>do u have video toturial about that project im begener and i need this .....</p>
<p>Hi .. I am doing the same but my output level used to be something like 1.67 v so it does produce a short. i am using lm 741.. please help</p>
<p>Hi .. I am doing the same but my output level used to be something like 1.67 v so it does produce a short. i am using lm 741.. please help</p>
<p>Awesomesauce! Another application might be a snail mailbox alert gadget! I have an old Verizon flip phone that used to be registered to what is now my new phone's number. I've been told that it only works for emergency calls. It never had a SIM card. Would that phone still work with this application?</p>
<p>My House Was Burglarized consistently about 4 years back, i tried this but did not get the right configuration, the circuit sucked, i was to buy an alarm system, this was very expensive, i was a padewon learner - now i am a Jedi, there are a few things i would consider adding to this circuit, a glass break or sound detector or motion or speaker configuration, that would be cool, but my configuration involved a relay, it sucked! Nice Job though! maybe we could collaborate!</p>
<p>it's a great, and your blueprints very nice. BUT, two things you don't solved:</p><p>1st - this phone do not reset a pressed key, and do not fast dial to programed number after you closed the door.<br>2nd - any alarm system must have a time for user to leave a room after armed</p><p>best regards</p>
<p>I was thinking about that .</p><p>I suggest keeping the switch outside the house where you may switch it on after closing the door.</p>
<p>Hi i like your idea of using a cellphone i think its awesome!!! just one thing what if i were to use a different op amp? for example lm741 or lm324 with that be okay too </p>
<p>Pretty much! It's a comparator, so you could use any cheap opamp or comparator Ics like LM311</p>
<p>exactly</p>
<p>One Question?</p><p>Why will a thief try to enter from a closed door or main entrance when he can do the same with any of the window in house..not a reliable system....</p>
<p>I have mentioned about it in step 10:Extending the circuit</p>
<p>they may enter through the window but they will LEAVE through the door. at least the guy who robbed me did. (as he carried my stuff out)</p>
<p>nice </p>
<p>This is the same our thesis when I was in University 7 years ago. we used the Nokia 3310 as our device and programmed with zlog</p>