Keep Our Pets Safe Act of 2018 This bill amends the Animal Welfare Act to prohibit a person from knowingly confining a common household pet in an enclosed space if the confinement could harm or kill the pet through exposure to excessive heat or cold, lack of ventilation, or lack of water. A common household pet is a domesticated animal (e.g., dog, cat, bird, rodent, rabbit, fish, or turtle) that is traditionally kept in the home for pleasure rather than for commercial purposes. The bill specifies the applicable criminal penalty—a prison term of up to one year, a fine, or both—for a person who violates this prohibition.