the flask is made from metal (stainless steel) so it will definitely trigger a metal detector. You probably need something plastic, the flask is made from metal (stainless steel) so it will definitely trigger a metal detector.
Flasks can be used for making solutions or for holding, containing, collecting, or sometimes volumetrically measuring chemicals, samples, solutions, etc. for chemical reactions or other processes such as mixing, heating, cooling, dissolving, precipitation, boiling (as in distillation), or analysis.
So, if you want to be guaranteed you're drinking from a safe, reusable, steel water bottle, look for #304 or 18/8 food-grade stainless steel. #304 or 18/8 food-grade stainless steel is safe at any temperature and won't leach chemicals into your water if it's scratched or ages.