IIRC you have to change the switches on the siren to reset it and to put it into learn mode. It's easiest IMO to lift it off the wall and work on it indoors (wrapped in cushions because of the noise). Photograph the dipswitches in your because there are (at least) two shapes of siren case.
It has at least one key-hole shaped screwhole in the backing plate to make it easier to take off,
Depending on your agility on a ladder, you might find you can fit it where you can reach it through an upstairs window for changing the battery. It has to be visible from the street and out of reach from the ground. Near the front door is good because you can the see and hear it when you enter and leave.
p.s.
photograph your control panel too and I may recognise it.
Hi John all sorted, found on the net another suggestion to learn the siren and worked first time going to see if there is another manual for the 6400 or 6200 as they may differ from the manual he has
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