https://www.michigan.gov/documents/UTC_50201_7.pdf (PDF page 17) said:
R 28.1458 Rule 458. Requirements when leaving motor vehicle unattended; violation as civil infraction.
(1) A person who has control or charge of a motor vehicle shall not allow the vehicle to stand unattended on any street or any other place without first stopping the engine, locking the ignition, and removing and taking possession of the ignition key. The provisions of this rule that pertain to the locking of the ignition and removing and taking possession of the ignition key do not apply to motor vehicles that are manufactured with an ignition system that does not have a key and that is incapable of being locked.
(2) A person who violates this rule is responsible for a civil infraction.