The 'PIR' is built in, and seems to be a diode looking through a small bit of the obscured glass surround that has been left clear. This beast is 'programmable via a remote IR control allowing you to set sensitivity, time on when triggered etc - a lot of permutations - in the fault mode it fails to respond to movement or its control. One of the early failures was 'always on' but all the other five have been 'no response'. Never heard a relay 'click' as in the old halogen ones, but then it is mounted up high - about
18 foot up on a gable end over a roller shutter door.Andrew