What type of notification appliance is designed for outdoor use?

Sounders are specifically designed for outdoor use because they are built to withstand environmental conditions such as rain, wind, and temperature fluctuations. Unlike other appliances, sounders can produce loud audible alerts that are essential in outdoor settings where ambient noise may mask the signal. This makes them effective for alerting individuals in external areas, ensuring that an evacuation or alert message can be heard over long distances.

Visual alarms, while important for indicating emergencies, are typically used indoors where visibility is clearer and less affected by environmental factors. Chimes are more suited for indoor applications as well, often used in situations like door entry notifications rather than fire alarm systems. 'None' does not apply here since sounders are indeed suitable for outdoor scenarios.