Have you ever ordered a diet soda, sipped it, and immediately doubted whether it was truly diet? Then you might find this little tip useful.

Whenever you’re not certain that your drink is diet or regular, try grabbing your glucometer, putting a test strip in it, dipping your finger in the drink, and wiping it onto the strip – just like you would do when checking your blood sugar. If the drink is diet, then you’ll know because your meter will display an “extreme low” result, or something to that effect. The key is to not panic and remember that it isn’t your blood sugar you’re looking at, it’s the sugar levels in the drink! It’s just the opposite in the case that your drink is regular/sugary – you’ll get a “high” reading that’ll make it obvious that your beverage isn’t what you ordered.

This trick has come in handy several times for me. Most recently, I was doing some Christmas shopping at the mall with my boyfriend when we decided to stop at the food court for some lunch. We split a chicken tender meal from Arby’s, which came with a medium soda that we could fill on our own.

I took on the task while he waited for our food, and was excited to see that they had Diet Dr. Pepper on tap (seriously, that’s rare for most fast food joints). I filled up the cup, fitted a lid on top, stuck a straw in, and took a sip. Hmm…it tasted sweeter than I thought it should. I mentioned this to my boyfriend as he picked up our food and we made our way to a table. I told him that I definitely got it from a tap that was labeled “diet”, but we both knew that just because the label says it is, it doesn’t guarantee that the right soda bib is hooked up to the proper line. (Our shared experience working at a movie theater several years ago clued us in to the fact that employees can make mistakes with this.)

He expressed his doubts, as well, and then it occurred to me to do the old soda test strip check. So I did, snapping a picture of the results and feeling reassured by the factual evidence that I was drinking a sugar-free – not sugary – beverage.