Abbott Freestyle Libre 3 continuous glucose monitors.
Brand new in sealed package.
All you need is one of these and a smartphone that's new enough to download and install the "Libre 3" app.
Recently expired -- 2/28/2025 -- but stored in a cool dry place and still working great. Used one a few weeks ago and it gave good readings. The adhesive held flawlessly for the entire 14-day sensor life (scrubbed thoroughly beforehand with soap and water, and again with rubbing alcohol).
Several available. $50 each.