Keep in mind that my knowledge of electronics is rather limited. To make a long story short, my house was already wired for a security system but the actual alarm system was never installed nor did I care for one. However, the prospect of playing around with an Arduino was too great to pass. I'm not trying to create a security system, just a system that keeps track of movement, doors opening and closing and so forth.
I connected the various security cables into an Arduino. These are all normally closed circuits. Reed switches for doors, PIR sensors, etc. I run one wire to ground and the other to an Arduino digital I/O pin, which I set to HIGH. This is with the assumption that it enables the internal pullup resistors.
The problem I see is that every now and then, when something is triggered, some other pin is also triggered. That is, a door opens and some pin sensing another door is also triggered. In addition, some times, when I switch a fluorescent light (the long tube with ballasts type), some random pin gets triggered as well. All in all, it all works fine. It's just that some times I get this "extra" triggers. The documentation talks about pins capacitively coupling the state of a nearby pin but I was under the assumption that the pullup resistor would handle it.
How to fix this?