Also, some DVR's have alarm inputs, so on a dvr that allows it you could link PIR's to your alarm to start a camera recording, this would have the advantage of giving a lot less false alarms on outdoor cameras (which will always be triggering the motion detection when a small cat runs across the yard, or tree branch moves, or some paper flies by on a windy day etc etc.)
nice theory, unfortuntely what you have typed is no use in this instance.
The OP wants a separate alarm from the cctv, but he did not realise a DVR has built in motion detect.
He could connect the alarm to an input on the DVR (but which one) so that it records at max frame rate for the duration of alarm activation, but whats the point, you want to see what happens
before the alarm goes off not after. ie see the person walking up the drive.
Dont think that pirs false alarm less than motion detect.
You can not use an ordainairy pir outside, so external use pirs are required, such pirs do exist (redwall is popular) but they too false alarm and cost a whole lot more.
£162.00 each