Protect your Room with your own Laser Security System!!!

A really easy and cool electronics project and lots of fun to play with once it finished.Its basically a laser tripwire but has a large application quotient in our everyday life's! so all you teenagers and mad scientists go out there and make your rooms and labs intruder proof :D

• Breadboard / Perf-board
• Transistor- BC 109 (or any equivalent general purpose NPN transistor)
link to the datasheet of BC109 :
• Wires for connecting
• 9 volt battery
• 9 volt battery clip
• 10k ohm resistor
• LDR- mine was 8k ohm

This electronic circuit uses a transistor to detect light falling on the LDR (light dependent resistor) to activate or deactivate an alarm (or any kind of electronic component). The two resistors (the resistor and the LDR) are connected in series and the common point between them is connected to the base of the transistor, making a potential divider. It uses the property of "threshold voltage" of the transistor to trigger the alarm. This means that we can set a minimal amount of light intensity to trigger the alarm. I have set it to the intensity of sunlight as the minimal. This means that, it won't trigger indoors in ambient light but only when there is a light of high intensity (like a laser). To set your own intensity or if you don't a LDR that is working with the current specifications then just replace the resistor with a potentiometer (or other kind of variable resistor) of something like 30k ohm. Then keep changing the value until you get the desired result.
A more scientific method will be to see the reading (resistance) of the LDR in the desired light. Check the threshold voltage from the datasheet and then used the potential divider formula to calculate the required resistance of the 2nd resistor.

Note: The relay is only used for simplicity. The output can also be controlled by power transistors, to control any other device.

Please feel free to pose any questions that you might have. And make sure that you comment, rate and subscribe.
Thank you :D

Views: 117629
Runtime: 5:37
Comments: 56

Tags for this video:

Find more videos in the: "28"
Uploaded by:
See more videos uploaded by


Author Rishi Balasaria ( ago)
Not yet. I am yet to finish my schooling. I actually did this long back in
the 10th standard If i remember right. But sure, happy to help regarding
any electronics projects...

Author Rishi Balasaria ( ago)
Yes, see my reply to 88magar

Author Rishi Balasaria ( ago)
Yes there are many ways to get the alarm to stay on longer. You may use a
microcontroller like an Arduino, PIC, BASIC stamp, atmel, AVR... or an set
of logic gates to set of the alarm and then control it with a switch to
turn it off. However the simplest and most practical would be to just use a
555 timer. You can even control how long you would want for it to be on.
Hope this Helps

Author 88magar ( ago)
thanks i just made my second electronics project,is there any way of
getting the alarm to stay ringing for longer?Thanks great upload.

Author Rishi Balasaria ( ago)
Well the solution is pretty straight forward... just exchange the positions
of the LDR and the resistor. It should work just fine.

Author Ardhendu Chakraborty ( ago)
hey...umm...I've completed my device based on your circuit... it actually
works...but the other way... if m focusing a laser light on it...the buzzer
goes off... and when i'm placing an obstacle between the laser and the
device....the buzzer doesn't make a noise... I checked all my connections
and they are just the perfect... not able to understand the cause of this
problem... some-one please help..!!

Author Rishi Balasaria ( ago)
Nah, i that will not work as the 9012 is a PNP type transistor and the
BC109 is a NPN type transistor

Author david shilo ( ago)
can i use transistor 9012

Author Sitha Sek ( ago)
how can i make the buzzer stay on for three minutes or so? i manage to get
it work like you but i want the buzzer stay on 1-3 minutes. is it possible?

Author rishabh uppal ( ago)
hyy bro u doing engineering??? whch help me??? eva i wannna do same like
these thing whch is related 2 dezzz.!!! cool gadgets..?? help me.??

Author Lynexen03 ( ago)
Oh thank god,... i finally make it work. at the first im using a MOSFET
IRFZ44 and that when the conflict happens.... i changed the mosfet to a
transistor and it worked... anyway can i consult u if any error will appear
in future...

Author Rishi Balasaria ( ago)
Ya sure! Would love to be of any help regarding the project. Please share a
little more about this project. I would need to know your objective, are
you protecting a room? a precious item? what is it? Also what you wish to
achieve by the end of the project? is there a specific understanding that
the project needs to convey/showcase?

Author Lynexen03 ( ago)
Can you help me with my project.. (BURGLAR alarm..) if ok.. here is my fb
( i really need help its requirements for me.. i need
to pass please..

Author Rishi Balasaria ( ago)
Its really hard to believe you! Most electronic appliances (except mobiles)
use an adapter run on 9v. A popular example being Computer speakers, the
auxiliary input speakers, run with a 9v adapter. Anyways answering your
question, use the same transistor. Try with same resistor if it doesn't
work replace it with a variable resistor (potentiometer) and set/tune it to
the resistance it works at. Or else see the threshold voltage of the
transistor and calculate the value of the resistor.

Author halone het ( ago)
hi my friend sorry i cant find any 9v output so i can find only 12v output
so please tell me which transistor and resistor to use please help me,

Author Rishi Balasaria ( ago)
Sure you can use a 9volt bulb. The problem is that bubs use a lot of energy
and will drain your battery rather quickly. So if you do decide to use a
bulb add a 9v power regulated supply so you don't need to worry about the
battery running out. "ldr of 12m"? what's 12m? 12mega ohms? Any low powered
laser will do. I used a simple laser pointer.

Author halone het ( ago)
hello bro i want to ask two question 1) can i use 9v light instead of
buzzer 2)can use ldr of 12m and which laser i hv to use how much watt.

Author Abdul Rehman ( ago)
okay.... :) thank you..

Author Rishi Balasaria ( ago)
You should read the info section just below the video. It has a fair amount
of detail as to the different components i have used, the operation and
utility. I have also explain the working in good detail. Maybe she should
do a little more research on the bare components. For example the
transistor- how it works, the history,etc... that should add a interesting
dimension and well as good depth of understanding to the report. Tell me if
you want me to explain more specifically. Hope this helps :)

Author Abdul Rehman ( ago)
I made the exact circuit as you made... and thanks to you it works
properly..... I made the circuit as a project for my sister who is in
twelfth grade....!! She just was asking if you could explain a little more
in detail about the working of this circuit and the components used so as
to help her write the project report.....

Author Abdul Rehman ( ago)

Author Rishi Balasaria ( ago)
I used a laser as it offers more range between the receiver and the emitter
than any led will. For the system to be effective there should be a
significant difference in light intensity of the source and ambient light.
Ultimately the choice of your light source really depends on your
application. If your only looking at the width of a door then yes a
infrared led should work. You do get LED's that are high powered and LED's
with in build lens for focus.

Author Nigel Menezes (1695 years ago)
can i use an infra red led ?? n how do i focus it on the ldr??

Author Rishi Balasaria ( ago)
Ya, relays can at times really get a little difficult to figure out (as
there are 5 points).An effective method to find out which point does what
is by simply searching for the datasheet online (just google the part no).
The datasheet will tell you which 2 points are the load (which you will
connect in series with the mains and light) and which 2 are the coil points
(you will in this case need to connect by a normally open configuration,
implying the light will only be on when the coil is high)

Author Noras Lalruatfela Chinzah ( ago)
Pliz can u tel me where to conecu the relay part to used in light system

Author kannam shashank ( ago)
i'm having 5v buzzer then which transistor and resistor are to be used.

Author Rishi Balasaria ( ago)
I am very sorry. If you upload a video of this quality with complete void
of focus, I really wont be able to help you out. I need to see to
understand the circuit, so keep the camera still giving a focus on the
wires, connections and the breadboard will make all the difference in the
world.Please check your buzzer by directly connecting it to the battery. I
really feel that you should once just try and arrange the circuit in the
way i have shown at the start of my video. See the schematic again.

Author Rohan Bhojannawar ( ago)
Sorry I gt the Exact O/P as expected...! i too designed xactly lyk u on a
LASER... its working..but i styl gta build it on PCB....SOldering OMG.

Author Rishi Balasaria ( ago)
Well, that's exactly what suppose to happen, the buzzer needs to stop when
the laser is falling on it and go off when there is no laser on it (to
indicate an external disturbance). its a "Dark-activated circuit".So will
only start the alarm/buzzer when there is darkness (or in our case when the
laser is obstructed). What do you want the circuit to do? if you could
explain me your goal, you would enable me to assist you better.

Author Rishi Balasaria ( ago)
One of the ways is to find your local electronics shop that sells
"electronics components and parts".Its crucial to search for shop offering
"electronics components" and not just electronics cause that would imply
electronics products.An easy way is to ask a electronics repair shop where
they source their parts from and anyways they would know the local shops.
Another way is to buy online on platform like ebay where you can get 20
LDRs for a dollar. Or dedicated electronics stores like digikey.

Author Rohan Bhojannawar ( ago)
I sumhow m nt gettin the output.......!!! The buzzer aint goin off when
laser is put on LDR Kindly HELP.........!!!!

Author Ghazanfar Uruj ( ago)
hey man where can i get LDR

Author Rishi Balasaria ( ago)
It would help if you could describe your apparatus. The specifications of
your transistor, resistance of your LDR, power source (9V battery?), Have
you used a breadboard or soldered in on a perf-board, etc... Or best you
could post a video response regarding the same.

Author Gurcharan Singh ( ago)
Thx bro it works

Author Rishi Balasaria ( ago)
Well, where you went wrong was the connections. Just interchange the
positions of the buzzer and the resistor and you should be good to go :D
When ever you face a problem in electronics especially when you dealing
with experiments like such at grass root level just go through the
schematic again. You will get rid of your problem. Hope this helps :)

Author Gurcharan Singh ( ago)
hey bro, i have made the security system but its not working properly.when
i put the laser light on LDR the buzzer go off and when i remove light form
LDR the buzzer is stop....plz help me to fix this problem

Author Rishi Balasaria ( ago)
Yes, true. If you are in doubt you should all ways look up the datasheet
for the component. It will greatly help you get your connections right. The
link to the datasheet for the BC109 has been added in the description.

Author Rohan Bhojannawar (1441 year ago)
In transistors where the notch is there is the emitter ryt ?

Author Rishi Balasaria ( ago)
Yep, soldering can be quite a challenge to get started at.There are a lot
of soldering tutorial on YouTube, you should find them very helpful. You
might also consider using a prototyping board (Perf board) rather than a
printed circuit board. They are very cheap allow for rapid prototyping.
Perf boards come in different orientations, some are in the same
orientation as the bread board, so you can directly fabricate the circuit
in the same orientation. Making the project a lot easier.

Author Rohan Bhojannawar ( ago)
oKh Thanx i dint hav a way to check dat out...nw i guess BRAD board can
do..? m in 12 fr which i gta submit electronics project I hav pland to
build xactly the same circuit as uas bt on a PCB...!! bt I aint finding
Soldering easy....

Author Rishi Balasaria ( ago)
the LDR i used was 8k ohms (as mentioned in the description). No there isnt
any rower rating on it. You will have use just use common sense to figure
where it will and will not work (so probably the maximum power circuit you
could safely use it with would be around 12-18volts and 2A max). As long as
you are using a battery you are good to go. a 1.5v AA, 9v, high power 4.5v
lithium ion/polymer battery's,etc... if You could explain your project and
your power source, that would be helpful :D

Author Rohan Bhojannawar ( ago)
what is Power ratings of the LDR used in ? is it specific ? reply ASAP gta
complete ma project....:P :)

Author Rishi Balasaria ( ago)
Ya, of course because of the simplicity of the circuit we can just directly
connect the components together. Using a pair of pliers (or bare hands) by
twisting them together. Or a more permanent solution will be to just solder
all the points (that need to be connected) together.

Author Chirag Patel ( ago)
buddy use an not gate ic so that wen any one cut offs the laser 1 goes to o
and den use

Author Adnan Khan ( ago)
i have a doubt that how do u use this breadboard

Author Abhishek Thakur ( ago)
Thanks budy really nice one

Author Rishi Balasaria ( ago)
ya, i know the way to make the system permanent :D a simpler way will be to
just use a AA battery pack. Actually given the time, i would actually
rather use a dvd burner laser diode with a laser driver (to increase my
effective range), or best use a IR laser diode and also run that with a
driver. That would make the laser absolutely invisible and wouldn't
obviously even show in dusty conditions. see the last part of the video
again, will see what i am asking :D

Author AakashMJ Sachdeva ( ago)
laser:Take the laser diode out of the laser light toy through a screw
driver which you have got..the mouth portion is the positive terminal and
the spring one is the negative terminal..connect both with a 9V battery
along with two 10k ohm resistors as the your laser light works on
connect this system with a switch..and stick this light in front of the
LDR..and you can also connect the buzzer with a switch..hope it was
helpful.. :-)

Author Rishi Balasaria ( ago)
Thank you :D tell me, what do you wanna know specifically? it a normal red
laser pointer. they come in all ranges of power and quality (the china ones
start at like 0.8$). For this kind of an experiment you don't need a
powerful fancy laser, cause even the normal lasers have a range of a
mile.However if you wish to made a real security system, (or something more
permanent) then getting a powerful, good quality one is the right way to go

Author armel mongane ( ago)
very helpfull!!but i need more detail about the LASER POINTER!!!!HELP

Author Rishi Balasaria ( ago)
thanks!!! :D actually i make this video quite long time back :P and i know
a way using logic gates, but was looking for a easier or a simpler way to
keep the alarm on, once it has been triggered. well, Glad you liked it :D

Author Anshul Aggarwal ( ago)
Sweet!!!! put for question in the form of an application! So right now this
tutorial can help you build a model for some application! Which is that
application that you are struggling with!! am sure your friends will come
up with ideas:) good going rishi!!!

Embed Video:


Search Video

Top Videos

Top 100 >>>


Analyse website