Mich. Comp. Laws § 600.2917a

Sec. 2917a. The owner or lessee of a theatrical facility where a motion picture is being exhibited or the authorized agent or employee of the owner or lessee who alerts a law enforcement agency of an alleged violation of section 465a of the Michigan penal code, 1931 PA 328, MCL 750.465a, and who takes measures, while awaiting the arrival of law enforcement authorities, to detain an individual who the owner, lessee, agent, or employee has probable cause to believe committed the violation is not liable in a civil action arising out of the measures taken unless the plaintiff shows that 1 or both of the following apply: (a) The measures taken were unreasonable. (b) The period of detention was unreasonably long.