Black Box FX810A-R2 Instructions Manual page 17

CAMPUS PAGER
When the batteries are low, the FX801A-R2 will beep once every 15 seconds
and the FX802A will beep once every 5 minutes.
The pager also maintains memory during a power loss, so you do not need
to re-enter its pager code (see Section 5.3).
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