If an alarm is enabled and Latch is not checked, the alarm will turn on when the level is exceeded and turn off again when the radiation level dips below the alarm level. If Latch *is* checked, the alarm will stay on once the level is triggered even if the radiation level dips below the alarm level. The only way to reset the alarm in that case is to uncheck Latch (when the radiation level is below the alarm setting) or to uncheck the alarm itself.