Explanation: The auto-alarm signal is a specific, internationally recognized sequence of two alternating audio tones (2200 Hz and 1300 Hz) transmitted for 30-60 seconds. Its primary purpose, as mandated by maritime regulations, is to activate auto-alarm receivers on other ships. This alerts their radio operators to an urgent situation, prompting them to listen for a subsequent distress call, such as an SOS message. An auto-alarm signal keying device automatically generates this precise, regulated sequence of tones and timing. This automation ensures the signal is produced accurately and consistently, which is crucial for reliable reception by auto-alarm equipment on other vessels. Option A is incorrect because the auto-alarm signal is a distinct tone sequence, not general Morse code. Option B is incorrect because the auto-alarm signal *precedes* the actual SOS distress message; it serves as an alert to listen for the distress. Therefore, producing the correct, specific auto-alarm signal is the device's exact purpose.