The Clicker is a cut-off light switch that Alan's mother gave him when he was a child because he used to be afraid of the dark.
The Clicker first appears in Episode 2: Taken in a flashback three years back. When the power goes out in Alan and Alice's apartment, Alice freaks out and Alan tell her the story of how his mother gave him the Clicker, and then gives it to her. She does not believe the story, but accepts the gift anyway. The Clicker does not appear again until the end of Episode 5: The Clicker, where Alan finds a shoebox in the The Well-Lit Room, Thomas Zane having made sure it would not disappear, even when he himself did.
Along with the clicker, Alan also finds a manuscript page that describes how he's standing at Cauldron Lake where Diver's Isle used to be and then clicking the Clicker. The page is narrated by the voice of Thomas Zane and also contains elements of Alan's childhood, suggesting Zane had an influence in 'creating' Alan's life with his writing (though this is refuted by Zane in The Writer DLC.)
Then in Episode 6: Departure, Alan does exactly what it said on the page, where he jumps into Cauldron Lake with the Clicker in hand. He then wakes up in a twisted version of his apartment, with a dark version of Alice Wake, where according to her, it is he who has the fear of the dark, but this is merely a trick. He then uses the clicker to drive the dream away. He then ends up at the Bird Leg Cabin, where Barbara Jagger is waiting for him. He holds the clicker where her heart should be and clicks it, where she burns away. The whole house lights up, ridding the darkness from it.
The Clicker has the power to drive away darkness just like Alan's mother had said. Whether this power was present all along or if it originated with the writing of either Zane or Alan is unknown.
When Alan first uses it inside The Well-lit Room, it seems like nothing happens, but when he leaves the power plant, he realizes it's not night anymore but in the middle of the day. Alan is not certain, but thinks the Clicker did this.
Later, Alan uses it when he stands where the island used to be and he jumps into the lake. After that, he wakes up in bed with a darker version of Alice, who tries to convince him it was all just a dream, but Alan does not believe her and then finds the Clicker to call for Thomas Zane.
Alan uses the Clicker one last time against the shade of Barbara Jagger, by putting it in the hole where her heart should have been and then clicking the switch to 'kill her'. This does not, however, destroy the Dark Presence, but merely the shell it was using.
At the end of Episode 5: The Clicker Alan finds a manuscript page that does not appear in his inventory. This page is about the Clicker.
"Alan, seven years old, would fight sleep to the bitter end. When he did sleep, he soon woke up, screaming the nightmares fresh in his mind. One evening, his mother, sitting by his bed, offered him an old light switch. She called it the "Clicker" and flicking the switch would turn on a magical light that would drive the beast away.
To imbue the talisman with all possible power, she added that it had been given to her by Alan's father. Alan never knew him and anything of his took on mythical proportions in his mind. With the Clicker firmly in his hand, Alan finally slept like a baby.
Now almost thirty years later, Alan thought of this as he stood on the rim of Cauldron Lake, the Clicker in his hand. He took a deep breath and jumped.
- Sam Lake said that the idea of the Clicker came from his own childhood, as he had the same toy to help him sleep. "To me, stuff like that always felt particularly mysterious and magical", said the creative director in an interview. "I love old rusted machine parts that you can’t quite figure out, old telephones and radios".