A shake can is a dog training tool that is basically a can with something such as rocks, pebbles etc in it that makes noise when you shake it.
A shaker can is an effective dog training tool that you can make yourself.
The noise distracts your dog, breaking them of the annoying habit of excessive barking.
The shake can is for exactly that: SHAKING.
It is a tool for getting a dog's attention and making him look at you.
Nothing more.
It's not used to frighten a dog and must NEVER be used to hurt a dog.
You can use a can with a lid and put some rocks or pebbles in the can and then put the lid back on and it becomes a shake can.
Shake cans can startle a dog when they are misbehaving and every time the dog is misbehaving you shake the can and the dog learns to stop the behavior.
Usually, one or two shakes with a verbal command will do the trick.
The verbal command reinforces what you want the dog to do.
It also works the dog towards the day when the can is no longer necessary.
Then you'll be able to say "Go", "No Bark", or whatever command you are using and your dog will actually listen.
Doing nothing rewards bad behavior.
Put a handful of pennies inside an empty water bottle, and when your dog starts barking, shake the bottle and say, "Quiet."
The strange noise will get the dogs attention and snap them out of protective mode.
Continue this for a week or so, and the dog will settle down without hearing the sound.