The Howler Alarm can have two different settings: sci-fi and default.
The Howler Alarm works well for telling you when your nuclear reactor is overheating (with a heat sensor) instead of building the more expensive Industrial Alarm which works better for intruders.
This item can be disabled by server mods - it can still be crafted, but you will not be able to place it.
To add your own sound, put it in the ".techniclauncher/tekkit/resources/newsound/ic2nuclearControl" folder in your appdata folder. Sound should be in ogg format and it's filename should start with "alarm-".
WARNING: If placed next to an active Redstone torch or lever for a long period of time, your game is likely to crash.