Searchlight

The Searchlight is a device used by enemies to detect Link's presence. They appear in the Forsaken Fortress in The Wind Waker and in the Infiltration of Hyrule Castle stage in Four Swords Adventures. Both places are, fittingly, locations Link tries to infiltrate. Link must use stealth to avoid being seen by the searchlights.

The Wind Waker
Searchlights are first seen in The Wind Waker as a part of the Forsaken Fortress's defense system. There are, in total, three pairs of searchlights in the fortress (making six in total). Each pair of searchlights is located on a turret of the fortress and is manned by a single Bokoblin. Should the Bokoblin encounter a distraction, he will lift the searchlight to the skies before leaving his post. He will return to his post as soon as the distraction disappears. If the Bokoblin is killed, the searchlight will be permanently disabled.

It is because of the searchlights that Link is sent into the fortress via catapult on his first visit to the Forsaken Fortress. If Link is seen by the searchlights while sneaking around the fortress, an alarm is sounded and Link is thrown into a jail cell. On his second visit to the fortress (when Link has his sword to defend himself), bombs will fire at Link and Miniblins will begin to attack him if he is detected by a searchlight. If Link hides underneath a barrel and remains still, the searchlights will pass over without detecting him.

One of the searchlights shines directly on the ledge beneath the window of the chamber where Aryll, Maggie, and Mila are held captive. Link must disable that searchlight to sidle across the ledge and reach the upper section of the fortress. Disabling the other two pairs of searchlights is optional.

Four Swords Adventures
Searchlights make their second and latest appearance at the beginning of the Infiltration of Hyrule Castle stage in Four Swords Adventures. They peer over the castle walls as the Links try to find a way into the castle. Much like in The Wind Waker, if one of the Links is spotted, an alarm will be sounded and Link will be thrown in jail (even the tune that plays in The Wind Waker as Link is being thrown in jail plays here).

The Links can avoid detection from the searchlights by diving underwater as it passes over them. If a Jar is shattered, the searchlights will promptly converge at the source of the sound. Although this may cause the Links to be captured, it can also be used as a decoy to sneak past the searchlights; if it is thrown away from the Links it will create a distraction for them when it shatters.