The One-Time-Only Module prevents the Two-Zone Alarm from activating a second time. So the siren will sound only once - and it won't become a nuisance.
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One-Time-Only Module - Photograph

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This is a photograph of the One-Time-Only Module. It prevents the Two-Zone Alarm from activating a second time. So the siren will sound only once - and it won't become a nuisance. This doesn't mean the building has to remain entirely unprotected. Anything connected to the module's output terminals - will continue to operate after the siren has been silenced.
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