The Stopwatch is a time-stopping device invented by Gyro Gearloose.
Looking more or less like a regular stopwatch, Gyro Gearloose's Stopwatch is a time-stopping device: switching it on freezes time worldwide except for the user and anything within a 10-meter radius of them. Once time is frozen, everything within the frozen area is riveted in place, immovable and indestructible.
Shortly after being invented by Gearloose in the 1950's, the Stopwatch was stolen by the Beagle Boys, who used it to attempt to rob Scrooge McDuck's Money Bin. The Ducks managed to stay within 10 meters of the Beagles, however, throughout a wacky chase through the frozen landscape. The Beagles were eventually stopped with a bit of trickery, and the Stopwatch was destroyed in the process.
It took no less than three decades or so for Gyro to return to the idea, possibly because he had lost the plans of the original Stopwatch or forgotten to make any in the first place. Finally, however, in 1987, he rebuilt a near-identical device in the Time-Teaser, which suffered a similar fate soon enough.
Behind the scenes
It is unknown if the Stopwatch possessed the latent capability to cause time travel, though it is likely considering that it was made along the same principles as the Time-Teaser, which did.