Temp. Alarm; Alarm Tone - Humminbird 748 3D Operation Manual

Temp. Alarm sounds when the water temperature detected by the Fishing
System reaches the Temp. Alarm setting, which is either set in degrees
Fahrenheit or Celsius [International Models only].
For example, if the Temp. Alarm is set to 58 degrees Fahrenheit, and the water
temperature falls from 60 degrees to 58 degrees, the Temp. Alarm will sound.
Similarly, if the water temperature rises from 56 degrees to 58 degrees, the Temp.
Alarm will also sound.
Alarm Tone selects the pitch of the alarm sound. A brief tone will be produced
as you adjust the Alarm Tone so that you can select the tone that you can hear
best.
Alarms Menu Tab

Temp. Alarm

Settings: Off,
[International Models only]; Default = Off

Alarm Tone

Settings: High, Medium, Low, Default = Medium
46
33-120 Fahrenheit, 0-50 Celsius