The short answer is that some are safe while others are not. The ones that can be used without causing harmful effects have to contain naturally found elements, such as boric acid, clove or others. This stuff has been used as an antiseptic for many years, meaning that is not toxic to humans or pets.
However, even organic materials can mildly irritate lungs and eyes, so it is better to keep pets away while you apply it on your yard. The products that are not safe come with instructions which will tell you how to use them in order to not cause any harm.