I have just started experimenting with the pi and I have a question (which may sound silly...). I have a simple security alarm system at home and I would like to extend its functionality by connecting "in parallel" the raspberry pi, possibly together with piface. So, I would like each PIR to connect to both the existing system as well as pi. This will allow me to gradually add functionality (eg. logging or sending emails on events, something that my current systems doesn't support) while keeping the current system for driving the bell, handling the keypad, powering the PIRs, making calls etc. Is this possible? Can a PIR physically connect to 2 systems? Do I need to build some kind of opto-isolation?
Thanks in advance for your help!