The Wristwatch Shield was a gift given to Percy Jackson from his Cyclops half-brother, Tyson. It was made by the Cyclops from his tinkering metal, and was mentioned to have a wristwatch disguise, excellent detail, and great strength.
It is a shield that is magically encased within a watch. When the button on the side of the watch is pressed, a full shield spirals outward, resembling a camera shutter. When expanded, the strap of the wristwatch becomes a leather brace that wraps around the user's forearm. The shield is polished bronze , has the width of four feet, and inside of the shield is coated in a soft leather. It has a series of engravings on it depicting the events that took place during the The Sea of Monsters. The pictures include Annabeth Chase slaying a Laistrygonian Giant disguised as a dodgeball player, Percy fighting the bronze bulls on Half-Blood Hill, Tyson riding Rainbow toward the Princess Andromeda, the CSS Birmingham blasting its cannons at Charybdis, and Tyson battling the Hydra, as he held aloft a box of Monster Donuts.
Before they leave on the Quest for the Golden Fleece, Tyson is seen working on building something small. It is presumably this as he later tells Percy he's sorry it wasn't ready in time for the quest. Percy is left wondering how Tyson can work with tools so small.
At the beginning of the second Chariot Race, Tyson gives Percy a wristwatch and tells him to press the stopwatch button when he needs it. When the Hephaestus' Cabin's chariot attacks Percy, he pressed the button and the shield opens up to defend Percy and Annabeth, destroying Beckendorf's sword in the process, much to Beckendorf's dismay.
Percy brings the shield out to defend himself from Dr. Thorn, whose projectiles managed to create multiple dents in it. Percy later contacts Tyson to tell him that it was damaged, and Tyson offers to fix it for him.
When Percy enters Poseidon's Cabin, Tyson is already there and presents it back to him along with a herd of mini bronze hippocampi on the ceiling. It was unfortunately lost in the Labyrinth when Percy hurls it at Kampê, to allow Tyson to escape.