Laser Alarm System Help

Thread Starter


Joined May 29, 2014
I'm looking to make a laser tripwire to entertain my kids. I'd rather not spend a lot of money, and this video claims it can be done for <20 which is great. The only problem is I don't have a specific parts list to make it and I'm not familiar enough with these parts to know just by looking at them. Can you guys give me a list of (specifically) what parts he used in this video/what parts will work for them?
Thank you all!

link to the video:

Matt D.

Joined Nov 10, 2013
He shows the schematic in the video with the components and how to hook it up.

I think you can buy these parts from Radio Shack.
102dB piezo siren
NPN Transistor 2N3904
1000uf Electrolytic Capacitor - this is polarized
9V battery
LDS Photocell resistor
5K ohm variable resistor aka potentiometer
perfboard to mount components
2 project boxes
Single pole single throw (SPST) switch
cheapest soldering iron that runs on household current

All this can probably be online for less.

And from

AixiZ Power Adapter 3.2VDC Output;

635nm 5mW Laser Module 12x30mm

This is pretty cool, but doesn't really give enough information for people who have never made any electronic projects.

I think you would be lucky to do it for less than $40. Just the laser module and power supply from is going to run over $20 after shipping.

If you want to try it and have any problems post back here and get the help to fix it. I'm not an expert but I think this is easy for the folks on here.

Also, does anyone know if a laser pointer can be hacked to run continuously for this?
And can't an old 5v power supply for a cell phone be used with a resistor for this instead of buying one?


Joined Aug 7, 2008
Post #1 schematic makes no sense, prob. same as post #4, same cost.
Found a laser module on Electronic Goldmine, G 19D31 , or maybe D is 0 ?, @ US $ 2.29, same with battery, G196D1 . Also a laser target kit which seems to have all of your receiver parts except for siren , C 6739 @ $7.50. I think they have a $ 10. minimum.
It is G19031, G19601 @ $ 1.99, also wall wart [ AC adapter ] G19115 6V, 500 mA, @ $ 2.99, add 100 ohm in series.
Last edited:

Thread Starter


Joined May 29, 2014
I would definitely buy EG's kit you posted, but I have no clue how to make it power a siren instead of light up LED's.


Joined Aug 7, 2008
After looking at the kit ckt. board, does not seem to have mugh of what you want [ 8 LEDs in parallel driven by 2 PNP's ? in parallel, at least that is what it looks like to me ]
Electronic Siren G19519 $ 5.00, or Tone Alert 12V, G17111, $ 1.79, or Audio Indicator G19721 $1.59
All other parts are probably here also.