CGM = continuous glucose monitor .. consists of a small sensor worn on the skin, often on the back of the arm but can also be placed on the lower abdomen, or the low back/upper butt cheek. It has a tiny thin needle that pierces shallowly into the tissue directly below the skin and remains in place for up to 15 days. It measures the glucose level of the fluid found in that tissue, a.k.a. "interstitial fluid". It does NOT measure blood glucose, because the tiny needle doesn't pierce into a vein or capillary. The sensor uses bluetooth technology to send readings continuously to an app on a smartphone, or similar separate device (my niece's partner is T1D; their CGM readings go simultaneously to smartphone AND insulin pump). More info about how CGMs work here .. https://my.clevelandclinic.org/heal...-monitoring-cgm

Note that this thread is about "over the counter" availability of CGMs in the USA .. previously were available only to diabetics and only by prescription. In Canada, CGMs have been available OTC (without prescription) since at least 2019 .. but of course, insurance will only cover for diabetic with prescription. They're very, very expensive!