Jammers

Jammers are machine blocks which help world owners to block several things they don't want.

There are 4 main kinds of them:

Items	What it does
Signal Jammer	Prevents the world from showing up in the world menu, and changes the world name in broadcasts into JAMMED!.
Punch Jammer	Prevents visitors from pushing and pulling each other by punching around.
Zombie Jammer	Prevents infected visitors from infecting others in the world.
Balloon Jammer	Prevents players from throwing War Balloons in the world.

There are also several other items which act like a jammer, but don't have the looks of one:

Items	What it does
Ghost Charm	Prevents ghosts from spawning in the world.
Guardian Pineapple	Prevents consumables to be used in the world; was added to prevent people from exploding pineapple growtopians in the world.
Firehouse	Prevents fires from spreading by instantly putting them out
Mini-Mod	Prevents people from dropping items in the world.
Xenonite Crystal	Blocking/granting Mods that the owner wants