Alternatively you can link a value instead of a condition. Values are best used for when an object has multiple states, for example:
door locked > door unlocked but closed > door open.
Values are a lot a lot more flexible than conditions because they have multiple different query operators that you can use, such as: is equal to, is greater than, is equal to or greater than, is less than, is less than or equal to, doesn't equal.
If it's something that doesn't have multiple states, such as an item that can be picked up, or it's something that just has an off/on state, then conditions are probably the way to go.