Only if the red light comes on is there any danger to employees.

只有红灯闪亮时才有危及职工的险情。

《牛津词典》

If your smoke detector is working properly, the red light should be on.

如果你的烟雾探测器运作正常，红灯应当亮起。

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Do the following to ensure the safe operation of your smoke detector: if your smoke detector is working properly, the red light should be on.

为确保您的烟雾探测器的安全运行，请执行以下操作：如果烟雾探测器正常工作，则红灯常亮。

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