Picture of Protect Your Home with Laserbeams!
Here is an easy to make and powerful laser alarm system that can protect your entire home, indoors or out! My inspiration for this project came from Brad Graham & Kathy McGowan. Watch the video for details and the Test Results. You'll be impressed. I hope you enjoy this Instructable.

Remove these adsRemove these ads by Signing Up

Step 1: What you need...

Picture of What you need...
1. 2 small project boxes
2. 1 1000uF 35v Capacitor
3. 1 5K Variable Resistor
4. Photocell
5. IC Board
6. 9v battery and clip
7. 1 N3904 Transistor
8. Toggle switch
9. Small mirrors
10. HandiTak
11. 12v DC Piezo Siren - 102dB
12. Aixiz 650nm 5mw 12X30mm laser
13. Aixiz 3.2v AC Adapter

Step 2: Build the Circuit

Picture of Build the Circuit
Build the circuit based on the diagram. I cut my IC board with a dremel to make it smaller so there was enough room in the box along with the 9 v battery.

Step 3: Install it...

Picture of Install it...
laser alarm_007.bmp
Install the circuit board and the 9v battery in the hobby box. Line up the photocell at the hole and hot glue everything in place. Also, attach the siren and run the wiring inside the box. Finish your solder connections with the siren.

Step 4: Build the Laser Housing

Picture of Build the Laser Housing
Cut 3 holes in your second hobby box. One for the switch, one for the laser housing and one small one for the wires from the AC Adapter. Run the wires from the AC adapter in the box. Install the swicth and hot glue the laser in place. Wire the positive end of the AC adapter to the red wire from the laser and wire the negative ends of the laser and adapter to the switch.

Step 5: Tweaking...

Picture of Tweaking...
Turn on the laser and point it at the photocell box. You will have to adjust the resistor so the photocell is sensitive to the laser pointing at it during the day. At night, when the laserbeam is broken, the siren will sound.
1-40 of 500Next »
fmitchell21 year ago
Does the siren make a loud enough sound! We would like to eventually uses it for a laser game. please help.
fmitchell21 year ago
It would be great if some one could create a demo on youtube displaying the actual project. like step by step. My son and I would like to make this project for the children at my job. Boys and Girls Club and it appears very difficult. Or if someone could walk me through it with baby steps. please need this project before monday
Also where can i find the materials? It would be nice to shope at one store. someone please help.
ivkeilic2 years ago
This a correct schematic
image laser.jpg
ivkeilic2 years ago
I think this is right.
Laser Alarm Schematic.jpg
sjumper0075 years ago
hope this makes this diagram easier to understand
Picture 2.jpg
There's still 3 connections to the 9v battery. I'm confused. :s
just tap them all in one. :) see voltage divider :)
where to connect the positive and negative in the battery
this is the correct skematic just swap the led for a realy or buzzer

if you wont the circuit to detect darkness instead swap the ldr and variable resistor places
Which transistor (Q1) I should use?
Which transistor (Q1) I should use?
hi, your skematic works well with led or buzzer for example but doesent activate relay for some reason, somebody noted that its AC and for that the realy doesent work. i tried to convert it to DC with four diods but this didnt help either. can somebody please help ?
have you checked to see if the realy can be triggerd on 9 volts
works fine with 9 volts, actually works even from 5 volts
this was the other circuit i found
oh, i just tested out this skematic and it worked fine :), used 5k ohm pot and 2n3904 transistor, thanks alot for that
no problem always glad to help
ok also wat current is used to hold the really open maybe the electro magnet needs more current then the transistor can supply
this might be the problem, it says 1A on it but i dont know if its min or max current for this relay to be functional
(removed by author or community request)
yeah the box with the arrow is the variable resistor the arrow would be the middle connection on the variable resistor they are 3 terminals use on of the outer ones and the middle one
pep27983 years ago
it all works but is backwards like when i shine light on photocell it makes the buzzer louder please help me

iam interested in making laser security system,so can u please send
me the steps and the things to use in making it.please send it to my
email (
amioten13 years ago
is it possible to instead use an indicator light instead of a speaker
but it then if ur far from the machine i can u know that intruder came
lazarzoltan3 years ago
from where can i get the photocell peoples?????
buy it from e-bay
nporter23 years ago

could someone please post a schematic for a 12v dc 1A power supply to 4.5v 45mA laser with a 'normally closed' output on it.

lazarzoltan3 years ago
I can use other transistor?
pizza19933 years ago
Hello everyone!I just want to built a similar protect system but i face off some difficulties.I built this ( circuit for laser receiver and this siren( but when the beam look the laser diode the output is 1.36v and when the beam is interrupted the output goes to 3v which isnt enough to drive the 12v siren.
Any Idea?

Thank you in advance!
a normal realy wouldent stay on you would need a latching realy that keeps the realy on when triggerd
I mean , CAN i ask you.. for the circuit diagram or connection
of all the given..?
hope this helps
that's the title MR. DASIMPSON
Ahh MR. DASIMPSON1981.... CAN i ask you.. for the circuit diagram or connection
of the given..? i saw that on youtube..
maremil1433 years ago
Ahh MR. DASIMPSON1981.... CAN i ask you.. for the circuit diagram or connection
of the given..? i saw that on youtube..
maremil1433 years ago
that's the title MR. DASIMPSON
My brother says the circuit is wrong, is he wright and if he is can someone send me wright circuit plzzzzzzzz . This is my email
umar abbas3 years ago
hey can i use this variable resistor....
1-40 of 500Next »