With all the advertisements combined with advancements in technology, almost each month there is a new tool on the market to keep your home safe.
But let’s take a ride back to the years of the 1970s and 80s, homes were hardwired, with aluminum strips that were glued to the windows and magnetic connectors that were placed on the doors. The wiring was using in a series connection, (with respect to a parallel connection), so that any cut in the loop would trigger the central unit to activate. Most times, it would be a high decibel alarm and in the later years, the connection would be hooked up to a central alarm company as well.
These types of alarm systems were easy to set up and although there were professionals who could do the installation for you, it just as easily could by done by anyone savvy enough to wire it themselves.
The alarm systems were available at any electronics dealer, such as the now bankrupt Radio Shack, and there was a host of accessories that were available, if desired.
Another, somewhat unorthodox method was (and still is, if you know how) to build it yourself using computer software that would be programmed to sense a break in the electronic current and consequently, react as per the programmer’s instructions. e.g. Sound an alarm, call someone, etc.
In the mid 1980s, there was a unique software application provided for the Commodore 64 computers, that would allow the user to program the system, using the Basic language (a popular, easy to use development program at that time). One of the computer output ports would connect to a device called a Vic Rel, a controller that provided input and output sensing, using six relay outputs and two optocoupler inputs, that would allow the wiring to connect to it on the external (output) side and then, it would connect to the computer port by receiving current to it on the input side.
So, the program would constantly loop via the BASIC command poke, and be silent, as long as current was detected through the Vic Rel and as soon as the current stops, the program would branch out to a function (then called a subroutine) and perform the specified action.
How does it detect a break in the circuit?
Remember bits and bytes? When a bit is detected by the computer (program) as a 1, the system is ‘on’. When it is detected as 0, the system is ‘off’. Going one step further, this detection is more specifically, a detection of electric current, so as long as the current is flowing, the program is seeing a ‘1’ and is silent. As soon as it sees a ‘0’, it branches to the function and perform what it was programmed to do.