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No security system is complete without lasers. So in this project I am going to show you how to build a laser tripwire alarm from a laser point, a couple of mirrors, and a few dollars of electrical parts. With this you can cover an entire house with an array of light beams. If any one of them is crossed it sets off your alarm. It can be a standalone alarm or it can be integrated into a larger DIY security system. 

Step 1: Safety Note: Working With Lasers

Cheap laser pointers that you find in most stores are generally restricted to 5mW or less. These are generally considered safe. However, it is still possible to damage your eyes if you are not careful. When working with lasers, it is a good idea to wear the appropriate eye protection.  Avoid looking directly at the laser diode. 

Also never point lasers at aircraft. 
<p>Hi, I am trying to do this circuit but instead of the buzzer I want to put a small speaker so that when the laser is interrupted, a sound of my own desire shall be played. Do you know of any part, circuit that will help me store the sound and make it play through the speakers when the laser is interrupted?</p>
<p>You could use any sound module. I like the adafruit mp3 player. https://www.adafruit.com/product/1790</p>
<p><strong>hello dear teacher :) (sorry if i sent this message one more time with another account .<br></strong></p><p>actually i made it about 8 months ago but now i want make some differences on it because it will be more useful to me,anyway.<br>i want know can i make it automatic!.. without use switch!..<br>my mean is JUST when something or somebody is between mirror and laser the sound be ON,<br>after that with coming the light on cds the sound will be OFF itself without pushing any switch,<br>and the system will be ready for next situation!<br>is it possible!thanks again</p>
<p>Yes. You can modify the system in that way. But you might want to have the sound stay on for a few seconds to make sure that you can hear it. Otherwise if someone moves through quickly, you might not notice the sound. For this you would want to use a 555 timer in monostable mode like this:</p><p> <a href="https://en.wikipedia.org/wiki/555_timer_IC#Monostable">https://en.wikipedia.org/wiki/555_timer_IC#Monosta...</a></p>
<p>yes, it's right</p><p>but i haven't this problem because i conected my laser pack to a remote annunciator, </p><p>and that remote annunciator with an small puls can start the sound and also continue it to several second,</p><p>anyway thank you so much for your guide and suggestion.</p>
<p><strong>hello dear teacher :)</strong></p><p>actually i made it about 8 months ago but now i want make some differences on it because it will be more useful to me,anyway.<br>i want know can i make it automatic!.. without use switch!..<br>my mean is JUST when something or somebody is between mirror and laser the sound be ON,<br>after that with coming the light on cds the sound will be OFF itself without pushing any switch,<br>and the system will be ready for next situation!<br>is it possible!<em><br></em>thanks again</p>
Hi thank you for these plans. I am wanting to adapt it to be a laser timer so a switch is tripped 100m away and timer starts then dipped when a multi beam laser system like one above is tripped. It would need to be very accurate and laser 3meters apart Outsode <br><br>Would you be able help with this ? Cheer <br><br>
<p>It is possible. But you can't get super accurate timing with a 555 timer. You would have better luck with a microcontroller such as an Arduino.</p>
As a beginner where do I start? Is there plans for something similar out there with the arduino
<p>You can search for Arduino alarms on the Instructables search bar. You might start by taking a look at this one: https://www.instructables.com/id/Arduino-Laser-Tripwire-Alarm-System/</p>
<p>You can start getting ideas here:</p><p><a href="https://www.instructables.com/howto/laser+alarm+arduino/">https://www.instructables.com/howto/laser+alarm+ard...</a></p>
Zero electrical experience here. Set up as near as I can tell based off our your picture, but the buzzer isn't sounding with switch in either position. Could you possibly help? Included pic of the setup I've got right now, did I miss something?
<p>I was wondering how to make this so that the buzzer is always off when the laser shines on it and always on when the laser is not shining on it. (as in it does not require a reset)</p>
<p>That would be a lot simpler. You could just use a voltage divider with a fixed resistor and a photoresistor. The fixed resistor would be connected to the positive voltage wire and the photoresistor would be connected to ground. The center wire would then be connected to the base of a transistor and the transistor would be wired between buzzer and the power wires. </p>
<p>I made it. Sorry simulated it in Autodesk Circuits. But i have also made it seems me ugly so i have posted the simulation images.</p>
<p>I just bought a pair of garage door laser sensors that stops the door from closing and can something more simple be made using these garage door beams so when broken it sounds a beep from a audio device? I thought of trying something basic and maybe a couple reflectors and thought it might be simple as breaking the beam and when it does sound a beep for like 5 seconds or something</p>
<p>If you want to use a 555 timer IC like the one used in this project you will want to wire it in monostable mode. The circuit will look something like this.</p>
<p>Thanks I will have to look into what the 555 timer is and what is IC? Dummy here on all this stuff. And monostable mode, all greek to me. My bro n law is pretty good with electronics and may be asking him for help on this also.</p><p>The garage door sensors have 2 wires each coming out of each of them, I have extra wire run in PVC to the garage so connecting them together won't be a issue if needed. The wire ran is 4 pair phone wire so maybe that will help if I need it</p>
How do i use logic gates to make up the circuit and what will be the use of it.<br>Im Sorry If Im annoying you but im actually new to all this...<br>
<p>Try using this circuit</p>
Thanks A Lot <br>Ill Get Back To You....
<p>Hi. I am thinking of using an old mobile phone USB charger (5V, 1Amp) as a power source for the circuit. Will there be a problem with that?</p>
That souls work fine.
<p>Thanks!</p>
<p>Hello Sir. I want to do this alarm system using Logic Gates.</p><p>What would it be like and it would be better if u could give me some good reference projects based on the same. </p><p>Thank You</p>
<p>There are a lot of ways that you could do this with logic gates. You could just recreate the 555 timer based on its internal schematic. Or you could make something similar using a simple OR gate, Just have one input be the resistor voltage divider and the other input connected to the output pin through a switch. When the switch is closed it acts as a self latching gate that will stay on when the photo resistor is activated. Then open the switch to reset it.</p>
Can u give me some reference for it
<p> what specifically would you like to know? </p>
<p>Sir Jason Poel Smith, I am a Grade 10 student and our group conducting this laser alarm for our research project. And we need to add a feature which is sending a text message to the owner when a intruder is detected. What should I do ? I really need your help please. Do you know the code for this sending of message ? Please reply Sir, I'm begging you PLEASE help us.</p>
<p>You are going to want to use an Arduino micro controller instead of a 555 timer. You will need a shield that is capable of sending text messages. There are several to choose from. To get you started, check out this instructable.</p><p>https://www.instructables.com/id/Intruder-Alarm-With-Text-Message-Notification/</p>
<p>Yes, it should be noted that SMS is an email system. If you are efficient in programming, you connect the arduino to your computer, have your computer collect serial out, and make your computer send an SMS.</p>
<p>how can this circuit be generated on multisim?</p>
Sorry but I am not familiar with multisim.
Hey man my machine just buzzes no matter what
<p>hello mates, really glad i found your design. In my case i need to make the object and the simulation (i'm using protheus). The problem is, when i press the button for resetting the alarm while the LDR didn't get the laser (Laser not used properly), the states became error and the output of ic 555 is changed between 0 and 1 rapidly? if that's normal, why it is happening? i need to make sure i can answer it on my presentation (my experimental became fruitless :( )</p>
<p>Sorry for the slow reply. Could you post a picture of your circuit. That would help me figure out what is going wrong.</p>
<p>look like it happens because the input of TR is changed between 0 and 1 rapidly, i dont know the reason tho, it happens when i changed it the input of TR from the switch to logic state (kind of tools to determine the state on proteus). and the output become a toggle if i change the state of TR from 0 to 1 to 0 continuously when the ldr isnt getting a light</p>
<p>Try using a different value for the resistor that is in series with the LDR</p>
<p>the left one (the others is my little experiment to measure ldr resistance</p>
Hey nice tutorial but it will be better if u add some better pics of schematics I mean the soldering side
Will 9v buzzer work
Maybe. Most buzzers have a range of voltages that they can operate at. Most will work at a lower voltage than they are labeled for. Or you can replace the power supply with a 9V battery. Just be sure that you don't try to power the laser pointer with 9V. That could damage it.
What should be the capacity of the resistors
Do you mean resistance values of the resistors or the wattage rating?
What should be the capacity of resistors
<p>PLease tell me where to connect +ve and -ve connection to this laser. Please edit the pic and mark the points where the connections are to be made.</p>
<p>Its always fun with Lasers . Thanks Mr.Jason Poel Smith for such a nice n interesting project. <br>I just used the Arduino Board as a power source . :p<br>I J</p>
How can I connect an lm 358 voltage regulator to the circuit because I am using a 9v battery and how can I connect use a variable resistor with three pins for R2
<p>As long as you are not connecting to a microcontroller, there is no need for a voltage regulator. The 555 timer circuit can operate just fine on 9 volts. To connect a variable resistor, connect the center lead to one point and either of the two side leads to the other. The remaining side lead will be unattached to anything. </p>
I followed the circuit diagram the alarm sounded when on. But when I pointed the laser pointer on the ldr it didn't work....how do I know if the ldr is bad

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Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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