This is about as close as you can come to a portable Star Trek tricorder these days. The SCiO is essentially a spectrometer that connects to your smartphone to tell you virtually instantly what the thing you are pointing it at is made of.
In practical terms for dieters, just pointing SCiO at food reveals its ripeness, number of calories and nutritional value. You’ll be able to scan plastics to ascertain their recyclability, home brewers will be able to more accurately monitor alcohol levels, detect what’s in that pill your doctor prescribed, what’s in those cosmetics, how healthy your plants or potting soil are, and discern the difference between a diamond and zirconium, fake from real leather, and real from counterfeit cash.
So it’s not as good as an actual tricorder, but it comes close enough. In the future maybe you will even be able to use devices similar to this to check your health, even test for cancer.
You can get one via their Kickstarter page for $200, if you hurry.