Abstract: A smoke detector that provides a battery warning arm that is pivotally attached to the smoke detector and is normally stored in a flush position within the smoke detectors cover. Upon the detection of a battery that is low, dead, missing, or not correctly aligned with its electrical contacts, the warning arm is released by a latch and swung down from the detector to display a luminous brightly colored instructional warning. When the warning arm is activated due to a low battery, the arm swings down and continues to swing in a pendulum manner to attract further attention. Even when the smoke detector's battery ceases to provide any electrical energy, the warning arm continues to warn persistently and cannot be repositioned to its stowed position until the detector has ample battery power. When deployed the warning arm exposes the battery and also a spare battery compartment whereby the warning arm also serves as a battery door.