The most popular ones are the Dexcom sensors and then the Freestyle Libre. Unfortunately you need a prescription for both in the US. Otherwise, if you'd like to monitor your blood sugar, you'll have to do it via a blood glucose meter and just space out your testing. You can buy those over the counter at any pharmacy/superstore and they're relatively cheap.

If you end up buying a blood glucose meter, the best way to get a good idea of your blood sugar movement in your body (if there is any) would be testing at several times throughout the day after specific events (like eating and/or exercising). Waking up (for fasting glucose), pre-meal (to get a baseline), post-meal several times (15 minutes, 1 hour, 3 hours). I would also experiment with how it reacts to different types of food and beverages. For example, try drinking a glass of orange juice and testing 5-15 minutes after. Some non-diabetics still experience very small blood sugar spikes from liquid carb sources.

I use the Medtronic Guardian Plus because it ties into my insulin pump which then regulates how much background insulin to give me. Dexcom, as mentioned in another comment, is a standalone sensor that doesn't tie directly into a pump.

All sensors that I know of are invasive though, so they have to be replaced every 7-10 days, which requires a needle and other things to cover it.

You could also just buy a glucometer (though you'd need a prescription for the test strips, at least in the US) than test once or twice a day and keep a log.

I think they all need to break your skin in order to test. I'm not aware of any continuous monitors that don't need some blood to work. I anyone is I would be interested.

Here's one https://provider.dexcom.com/education-research/cgm-education...

Also an interesting article about people hacking together their own artificial pancreas https://medium.com/neodotlife/dana-lewis-open-aps-hack-artif...