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.
If you're only mildly curious and don't wish to invest much then you might consider urine test strips. Very cheap, but the reading is also very vague also. However, they will let you know if you have a problem or not.
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.