Squirrels very rarely die from exposure to rat poison because they have a different body composition than rats and mice do, they rarely eat poison and their indoor eating habits are different than those of other rodents. There is no legally registered poison for killing squirrels in the United States.
There are several different methods for poisoning squirrels, although each of them is rather ineffective. Anticoagulants kill squirrels over two to three days by triggering severe anemia or hypovolemic circulatory shock. The Just One Bite brand of mouse elimination poison works much more quickly, as do other common poison mixtures that involve chemicals such as strychnine and chloralose.