HOW to convert signal level for external-siren

["nitro2" <nitro2-remove-this-@xxxxxxxxxx>]

How can i convert a "positive hold-off " to a "negative hold-off" level.

The siren who was attached to my alarm has been taken of the system when i
moved , now i want to reinstall this siren BUT obviusly the ( un- )
installer has removed some components from this connection inside the
cabinet.

The only thing i can say is that now as soon as i connect the siren to the
cabinet ( outdoor siren connection ) it starts to work straight away , and
only goes silent when the alarm is ACTIVE .

the only info i got from the old installer is that i need to " use 2 diodes
to get it right " , so i am positive he knows what he removed since the
alarm was working without any problems in my previous home .

the alarm is an aritech cd150 .


who can help ????????