Most Gadgets have their limitations. The Sonic Screwdriver cannot open deadlock seals and psychic paper doesn’t work against people with psychic training. A Restriction is a specific limitation of the Gadget’s current function, not a list of things the item doesn’t do. For example, though the Sonic Screwdriver can do many things, it can’t make a good cup of tea. This isn’t a restriction, as the Screwdriver doesn’t have a Brew Tea function!

The Restriction should be discussed with the Gamemaster: it should be something reasonably common, but not so common it makes the device useless. Does it not work through lead? Need a special type of fuel to operate? Tricky controls so that only one person can use it? These are all great Restrictions that can make the device more interesting and cheaper for the character to purchase or create (though a Gadget will never cost less than 1 Story Point).