While underway, pirates are known to begin probing commercial ships as they pass around the Horn of Africa. The vast majority of probes and attacks are at night, although pirates are also known to hide in the fog during they day. The maritime security contractor on shift at night monitors the Automatic Identification System, or AIS, radar on the ship, and when he gets a blip on the screen he begins looking for pirates, usually in stolen fishing vessels, with his binoculars. In high winds, the older AIS systems will get feedback as they may read whitecaps out in the ocean, giving off false signatures and making it difficult for contractors to discern real threats.
AIS was originally developed for aircraft flying in and out of San Diego to help them avoid mid-air collisions during thick cloud cover. The system worked well enough with airplanes that the harbor started making use of it as well, and then the International Maritime Organization was lobbied to make it mandatory for all vessels over a certain size.
The AIS is essentially a line-of-site VHS receiver and transmitter that has an electronic display chart, about the size of an iPad, mounted in the bridge, which shows ships in the area and lists their heading, speed, and callsign. It will display this information to other vessels even when turned off, so the bad guys have to completely disable their AIS to remain undetected.
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