Hi

I installed a optima G4 in place of existing faulty alarm. As it was only a basic system I upgraded the system by installing additional PIRs. The PIrs are honeywell Activ8 and have a internal built in resistance on the alarm contacts of 17 ohms giving approx 20 Ohms on the loop.            Also I installed 2 PIrs in series for zone 2 to allow entry/exit inhibit for front door and side door, this doubling the loop to 39 Ohms. The manual does not mention zone resistance and the diagrams just show N/C contacts. Is there a max resistance on the input zones?                     Door entry and window contacts are just a few  ohms wire resistance.

Wouldn't recommend pirs in series, after a fa how do you know which one went off ?

agreed. It will work like driving with no windscreen but its not best.

If you need more circuits use a bigger panel

There will be a resistance threshold for closed loops but the lower the better, usually it's around 100-200 which you don't want to be near, but will vary on panel.

Issue is diagnosing future issues when you have multiple devices on a circuit, as above.

Thanks for the replies, i know it was not ideal using 2x pirs in series. But I can free up a zone (Window contacts) and connect PIR in that room in series with the window contact, therefore ie zone 4 PIR+ window contact . That would allow the entry/exit zones to have their individual PIR (Timed). I was more concerned about the loop resistance. All loops then would be in the 20-22 Ohm range, except for door entry

If there aren't enough zones it needs a bigger panel.