The 6-foot-3, 205-pound Harrison was offered by Alabama earlier this summer and made two trips to Tuscaloosa over the past two months. He chose the Crimson Tide over LSU and North Carolina, the school he had been committed to since before his junior season.
Harrison, a standout for Florida State University School, announced his commitment at a high school media day in Tallahassee.
In the 247Sports composite, Harrison is rated as the No. 205 prospect and the No. 9 overall safety in the country.