Colo. Rev. Stat. § 18-4-407
If any person triggers an alarm or a theft detection device as defined in section 18-4-417(2) or conceals upon his person or otherwise carries away any unpurchased goods, wares, or merchandise held or owned by any store or mercantile establishment, the merchant or any employee thereof or any peace officer, acting in good faith and upon probable cause based upon reasonable grounds therefor, may detain and question such person, in a reasonable manner for the purpose of ascertaining whether the person is guilty of theft. Such questioning of a person by a merchant, merchant's employee, or peace or police officer does not render the merchant, merchant's employee, or peace officer civilly or criminally liable for slander, false arrest, false imprisonment, malicious prosecution, or unlawful detention.
C.R.S. § 18-4-407