S.D. Codified Laws § 55-1-49

Notwithstanding anything to the contrary in §§ 55-1-46 to 55-1-51, inclusive, a no contest clause is enforceable against a beneficiary to the extent the beneficiary elects to contest or otherwise challenge the settlor's signature whereby such a challenge does not in any manner constitute good, probable, or reasonable cause if the settlor's signature was witnessed by nonrelative witnesses or a duly qualified nonrelative notary public or both.