Hi,

Our house came with a professionally fitted (i.e. not DIY) alarm when we purchased it. As the house is a Lockwood the alarm has wireless PIR's (i.e. Lockwoods are a wiring nightmare).

Recently one of the PIR's seems to be misbehaving and setting the alarm off for no reason. I know which one it is and set the system to exclude the PIR but it still triggers the alarm - I believe there is tamper detection in the PIR's as they tend to go off if I replace the battery (I think this is what is triggering the sensor to activate the alarm).

The company who installed it no longer exist. I'm wondering if I can get a replacement PIR and whether they are easy enough to add to the system (the misbehaving one will need to be removed from the system too). I see they have different frequencies, how do you figure out which ones are compatible? 

I don't have the model number of the alarm on me but I believe it is a branded (by the installer) version of this model;

http://www.aap.co.nz/shop/Alarm+Systems/Kits/ELITE+S+LITE-1.html

So the questions are;

1) Is this a DIY possible job?
2) Should I just ring some alarm installers?
3) Just dump the system and get a new one?

Thanks all :D