Theresa Ehlers and her family are serious about keeping gluten out of their home. Just ask her pets -- her dogs, rabbits and parrot all eat gluten-free food.

Ehlers' family has banished the protein from their diets, household supplies and hygiene products since 2013. That's when doctors diagnosed her daughter with celiac disease, an autoimmune disorder in which eating gluten can lead to damage in the small intestine and cause digestive issues in the short term. Ehlers' husband is allergic to wheat, barley and rye (grains that contain gluten), and Ehlers herself has a sensitivity to gluten. They avoid restaurants for fear of cross-contamination. They scour ingredient lists on packages. They research products that have a gluten-free stamp to verify their claims.

So when Ehlers, a fiber artist, first heard about the Nima gluten sensor, she thought she'd found a tool to help her family navigate a gluten-filled world. The Nima is a handheld, Bluetooth-connected device that analyzes tiny samples of your food and tells you if it detects any gluten in what you're about to eat. She preordered a unit and agreed to participate in a test group for the manufacturer.

"I was really excited about the sensor," she said. "I thought it was going to be this huge tool for us to feel more confident."

At first, Ehlers and her family were happy. The Nima showed that the foods Ehlers tested that were labeled as gluten-free lived up to that claim.

Then, she tested a sample from a box of certified gluten-free crackers. A picture of a grain of wheat popped up on the Nima, the signal that the device detected gluten. Ehlers tried a sample from another box of the same crackers, and this time the Nima said it was gluten-free. She went back to the initial box, tested a new sample, and this time the Nima contradicted its first finding: no gluten.

Nima representatives told her it could've been an isolated area of the box of crackers that contained gluten. But the discrepancy was enough to make Ehlers question the device's accuracy. If she can't trust it when it says a food is positive for gluten, "how can I rely on it to tell me that's it's negative?" she said.

Ehlers' experience, along with the input of folks in the gluten-free community and a food scientist, raise concerns about the Nima and the future of devices that test for food allergens. Other users have taken to blogs and social media to tout the Nima as the tool they've needed to feel more secure that what they're eating won't make them sick. What do these dueling opinions show? It's damned hard to make a gluten detector that will address everyone's concerns.

A smart gluten detector is low-hanging fruit when you consider that gluten has become a hot topic in food culture. The Celiac Disease Foundation estimates that 1 percent of people worldwide have celiac, and that doesn't include people who have allergies or sensitivities to gluten. There's been such a growing awareness of the disease, too. Many packaged goods and restaurant menus will let you know if there's gluten in a product or dish.

The $279 Nima first became available for preorder in 2015. Here's how it works: You place a pea-size sample of the food into a Nima capsule, screw on the lid, and put the capsule into the sensor. You press the capsule's only button to mix the food with a solution at the bottom of the capsule. (You can't reuse the capsules, and a capsule subscription ranges from $60 to $120 a month depending on how many your order -- roughly $5 per unit.) That mixture reacts with a test strip on the capsule (kind of like a pregnancy test), and the sensor reads the strip for you. A smiley face means your food has less than 20 parts per million of gluten, the FDA definition of gluten-free. One wheat stalk means the Nima detected low levels of gluten, and two stalks means there was a high level of gluten. (In the next few weeks, the company will switch to a more general "gluten found" alert if the Nima detects any level of gluten.) You can share your results in the iOS app so other users can see which foods and restaurants have items with or without gluten.

Nima plans to create versions of its product that will detect other allergens like milk and peanuts, the latter of which is set to launch in fall 2017.

It will only be a matter of time before we see a competing gluten sensor or other allergen-detectors. But there's concern that those with severe or even deadly food allergies will wrongly place all of their faith in a product that lacks the accuracy you'd get from full-blown lab testing.

"These devices might give the user a certain sense of security as they go out and about trying different foods in different environments, but as a scientist I would be afraid that it might be a false sense of security," said Thomas Grace, CEO of Bia Diagnostics, a Burlington, Vermont-based food testing facility.

Nima CEO and co-founder Shireen Yates said the Nima is an additional tool for people with gluten allergies, not a replacement for the methods they already have in place to find gluten-free food.

"Thinking that one tool, one data point, will encourage them to throw caution to the wind does not give them enough credit," she said. "People with special diets are smart, educated and savvy; and they crave even more information to make even better decisions."

That's the way Michelle Bock approached the Nima. The creator of the blog Goodness Gracious Gluten Free was diagnosed with celiac disease 11 years ago. She received her Nima in January and tested everything in her house to verify that it was gluten free; she estimates she went through more than 130 capsules. Some foods she ate every day, like the protein powder she dropped in her smoothies, tested positive for gluten despite labels stating otherwise, she said.

It's been 17 days since Bock got rid of everything in her home that tested positive for gluten. For her, the Nima is worthwhile.

"It's been life changing," she said. "I feel better than I have in years."

The teeny sample that you use in the Nima pales in comparison to how labs test foods for gluten. During gluten testing at Bia Diagnostics, Grace said his lab finely blends an entire container of food among other steps before they test multiple samples from it. That way, any gluten contaminates would be evenly distributed and therefore show up in every test. In theory, the most effective way to see if there's any gluten in your box of, say, gluten-free cereal, you need to grind up that whole box and test at least three samples. And the device you test your food with needs to have been prevalidated to detect gluten, Grace said.

Food is more diverse and complex than other substances you might test, Grace said. Because of that, "I doubt that a device can be found that can be used by a consumer in a restaurant or even in one's home to give 100 percent or even 80 percent accurate results," he said.

It's also easy to pick up contaminants if you aren't in a controlled, that is, gluten-free environment. Here's an example: I ran a test in which I poured some Club crackers that contain gluten into a bowl, removed them from the bowl, then dumped in some gluten-free crackers without cleaning the bowl first. A sample of a cracker from the bottom of the bowl showed up on the Nima as having a low gluten level, most likely from a stray crumb from the Club crackers. But a gluten-free cracker from the top of the pile didn't appear to have any gluten -- a smiley face popped up on the Nima to indicate that it was safe to eat. Here's my beef: If I'd only tested a cracker from the top, it wouldn't have picked up the fact that there were crackers with gluten contamination at the bottom of the bowl.

Tricia Thompson, a dietician who runs the website Gluten-Free Watchdog, has conducted her own testing of the Nima. She said the sampling method isn't sufficient enough to detect gluten if there's been spotty cross-contact or uneven contamination, and she took issue with the distinctions between low- and high-gluten foods.

Nima provides tips to users through emails and on the company's website for how to get the most accurate sample of food that you can. For example, here's what they recommend for a slice of pizza: "We suggest taking a slice and cutting off a little bit near the tip of the slice so you can get crust, sauce and toppings in one sample. (Remember -- don't use more than a cumulative pea size sample.) You can take a topping piece and drag it around in sauce and other toppings before you put it into the capsule." But what if an edge of the pizza came in contact with gluten, but that's not the side from which you tested? Do you need to test every slice of pizza?

"In addressing the issue of sampling more broadly, hot spots are very common in both restaurant and packaged foods," Yates said. "One cracker might be gluten-free, while the next box might have contamination. French fries might be fried in a dedicated gluten-free fryer, but there could be contamination from the ketchup bottle on the table. No test can guarantee that every future box or dish will be gluten-free, which underscores the very real need for consumers to have tools like Nima they can use on an on-going basis in the real world."

And Yates agrees that gluten contaminants could get into a Nima sample, but "if a crumb on a countertop gets into a packaged food, that crumb can also get into a person's mouth," she said.

"We are giving information to the person about the food in front of them," Yates said. "Nima is not intended to attack brands or restaurants -- it's simply giving people the power to avoid the foods they want to avoid."

Bock agrees. Rather than feeling paranoid, she said she's less worried when she goes out to eat or tries a new packaged product.

"It gives me a little bit of a peace of mind," Bock said. "It's like my little gluten detector that makes me feel better."

Though they had different opinions about the Nima, Ehlers and Bock agreed that folks with celiac disease or gluten sensitivities need to have more than one method to determine if their food has gluten, and the first step should always be to read the ingredients. Ehlers double-checks a product's gluten-free label on its website, where ingredients are likely to be updated faster than on a box. Bock uses an app to scan barcodes and access info about whether or not that food has gluten.

"It's a lot of common sense and research," Bock said. "And Google is amazing."