Okay, I was gonna keep quiet on this one because I looked at it as a hobbyist doing a project on a breadboard or something. Now that some of these guys are treating it as if you're actually trying to build a working burglar alarm system, I'm going to put in my 2 cents worth. I speak from over 40 years of experience in installing, servicing, troubleshooting and fixing burglar alarms, starting around 1975. Most of that time was spent in servicing systems, so I got a lot of experience with systems that were installed decades earlier. In that day, users tended not to upgrade every few years--they expected the systems to
last, which most of them did.
Building an practical working burglar alarm from scratch (our of simple electronic components). one that is intended to deter burglary from a home or small business, is not as simple as it looks from any electronic schematics you're likely to find in a beginner's electronics hobby book.
The particular schematic you've referenced, for instance, doesn't even give a means to arm and disarm ("turn on and off" or activate/deactivate) the system, unless you're planning to remove the battery when you don't want it active. When you put the battery in--assuming the circuit board is inside the house, and any access door/window is on the protected loop--then you can't leave unless you add some extra circuitry to bypass a door to let you out.
Arming/disarming and means of access are crucial to a practical alarm system and are missing in your schematic.
Aside from that little detail, the schematic is one of the worst proposed designs for a burglar alarm that I've ever seen. It's understandable, because the EKI Project No. 12 schematic was designed to demonstrate the (hypothetical) use of an SCR rather than design a practical burglar alarm system.
The Project No. 12 design, with an arm/disarm means and a sounder added, would be approximately the equivalent of an Ademco model-100 control and system that I used to work on, well into the '80's, but was first marketed before my time, I would guess sometime in the '60's or even the '50's, I don't know.
The Project 12 design is simultaneously more complicated and less efficient, as well as potentially higher maintenance than the Ademco Model 100. I seriously doubt than anyone ever actually manufactured that design for commercial use. The Model 100 consisted of two relays and a key switch and lasted, for all practical purposes, forever (with battery replacements).
I never saw a Model 100 fail--every replacement was because the user wanted some feature(s) that the 100 couldn't be (easily) modified to give. It's too primitive for a home alarm today, but might be considered suitable to install in an isolated shed, The control panel consisted of two relays and a key switch; and door/window protective loop switches and a sounder of some kind completed the system.
@jacobi, if you're seriously trying to find a bare-bones, super-simple alarm system that you can build from scratch, let me know and I'll give you the best advice I can.
