The NMEA Service continuously monitors if an AIS target is in alarm mode.
If this is the case, three types of notifications are triggered based your AIS parameters:
- the target in alarm mode turns red, the map will eventually center on the target
- an alarm will sound if the Play sound on alarm option is checked, the CPA and TCPA of the target satisfy the conditions of distance and time to CPA, the alarm has not been acknowledged recently. The sound will be different depending on the class of the AIS in alarm.
- an alarm message appears on the screen. You must acknowledge receipt of the alarm by pressing the button under the message. The target remains red and the alarm stops. The message will show, amongst other parameters the CPA, TCPA and if the target crosses in front or behind us.
Here is an example of an alarm situation. We are sailing in the bay of La Rochelle towards the Ile de Ré. We see a sailboat on the AIS, class B, at 2:00PM and a tanker, class A AIS, at 11:00AM. Two CPA alarms are raised, first for the sailboat and then for the tanker. Both cross in front of us at a reasonable distance. We do not modify our heading for the moment but we keep our eyes wide open.
  
 