Mo. Rev. Stat. § 579.088: Fentanyl, devices to detect the presence of permitted.

Notwithstanding any other provision of this chapter or chapter 195 to the contrary, it shall not be unlawful to manufacture, possess, sell, deliver, or use any device, equipment, or other material for the purpose of analyzing controlled substances to detect the presence of fentanyl or any synthetic controlled substance fentanyl analogue.