The detector uses visual queues instead of only noise to alert you of problems. When the light in the center is green, everything is normal. When there's a problem, the device turns red (shown above) and issues a vocal alert as to where and what the problem is (ie. "smoke in the living room") and can operate in English and Spanish. If the light is yellow, that means attention is needed, such as replacing a battery.
Watch the video for an overview of the features: