No reliable way to test there is a handheld sensor but its 25 dollars per test and is so accurate down to 2ppm that it throws a ton of false positives on GF items. So not worth messing with. I can tell within an hour I’ve ingested contaminated food. Symptoms last days. Its miserable when your body attacks itself. It breaks your body down quickly over time. Pay attention to thirst, digestive upset, fatigue, brain fog, everyone is different as its an autoimmune disease. Get in tune with your body. How old are you? Also try to find out who in your family it came from and speak with them. Get family tested if you don’t know. It’d genetic. Keep a food log is the best way and don’t change items you consume more than one new consumable per day or you won’t know which in your log affected you and trial and error that kills your body isn’t fun to do. If your young you might not know contammed food right away but as your bodies reaction gets worse and breaks down overtime and the gut microbiome changes to your new GF diet your symptoms and notice will likely change. Find a well rounded vitamin supplement keep up on vitamin level checks in your bloodwork as you likely will become deficient over time of whatever your body needs. Hidden sources of gluten are in everything it seems. Toothpaste, soaps, shampoos, detergents, dishsoaps, other things besides food and drinks. Mostly due to poor manufacturing or transport practices. Again 1 new item per day. Don’t change what you consume all the time. Learn, read or watch videos. Just because you don’t feel the affects now doesn’t mean it won’t pound your body over years until your suffering daily just to maintain. Some people fair better than others so my POV is for someone like me. Super sensitive and debilitating lasting effects.