Any merchant who is a licensee under this title, or the merchant's employee, who has reasonable grounds to believe a person under the age of twenty-one has illegally purchased, attempted to purchase, or possess alcoholic beverages or has misrepresented the person's age with the use of any document for purposes of purchasing or attempting to purchase alcoholic beverages from the merchant or the merchant's employee, may detain the person, on the premises of the merchant's establishment, in a reasonable manner and for a reasonable length of time:
SDCL 35-9-2.1