I normally do calibrations on my Dexcom, so I don’t know what happens with entering the Dexcom sensor code and using Loop.
It’s about midnight now and I need to start a new sensor. I don’t want to be up at 2am entering calibrations. 
If I enter the Dexcom sensor code and start a sensor, and I put Loop in closed-loop mode… after 2 hours will it automatically pick up my CGM numbers and start Looping? Do I need to do anything else, or can I go to sleep and it will start Looping by itself?
Thanks!
If you do not calibrate every 20 minutes, you will get a red loop. That will stay red for the remaining warmup time and then once the cGM registers the first number, loop should pick it up and turn green and begin working on its own.
I have never done this but in theory what I’ve stated should occur.
Cool, thanks a bunch @ClaudnDaye!
This is uncharted territory for me because I don’t normally start a sensor so late at night! 
Update me when you can! How’d it go?
Hey, it worked! Loop did its thing last night while I was sleeping. Good to know, right?!
In general I am not a big fan of the sensor code. This morning my BG was 50 on 2 different meters, but my Dex said 70.
But in this case it made it a little easier for me. 
Thanks for asking!
@Eric what @ClaudnDaye said! Geez, you guys resolved that well! I have no issue with my supply, but always try to go the distance (72+8 w/pods, 10 days w G6) no matter the timing of replacements. Has meant some wonky night time results w/sensors. May try the G7 w/ next appt w Endo and gain some flexibility.
When looping, do you calibrate at this point? Or later when your BG is in range and level?
@Eric this is so interesting – I ONLY start a sensor so late at night! I know you all are so much more technical than I am with looping and pumping, etc – I only have the CGM to think about, but I let a “blank” sensor sit empty for at least 12 hours and then start 'er up to warm up when I go to bed at around 1am so that my data-free hours are in the dark hours of the night (where hopefully blood sugar is holding steady). So interesting how differently we all manage. I actually just did all of this last night! Glad that the loop kicked in and everything worked well for you last night.
In this case I removed the transmitter, waited 15 minutes, and did a sensor re-start. But that’s just because I wanted to go back to calibrations and not use the code.
In general, I calibrate no matter what my BG is, as long as it is not moving up or down super fast.
I don’t believe in the idea that you should only calibrate when it is within a narrow range of 80-120, which I have often heard people say. I think giving the Dexcom an idea of a high and a low is useful for it.
Wow, it is really interesting the differences we have. To me, the most valuable time for a Dex is when I am sleeping.
When I am awake, I generally know what my BG is and don’t need the Dex that much. But if I am asleep, I really need it much more, because I won’t wake up from a low all the time without the beeping!
Last night was an exception. The night got away from me and I needed to put a sensor on, but it was kinda late. 
FWIW And I’m inserting new sensor 20-24 hr before starting because the bg graph had become choppy if I only had the sensor in 8-12 hr before starting it. I try to get it started by 7 pm so I can get it calibrated before I go to bed.
I keep reading of “pre-soaking” sensors. I don’t have the problem of G6 being overly jumpy except for the first day, so I haven’t paid a lot of attention except to note the issue. But, I’ve always questioned whether pre-soaking doesn’t limit the useful life of a sensor. Please note: I’m not contradicting or telling anyone they’re wrong, but if someone knows, please confirm/correct my understanding of the science behind the process of CGMs. Here’s my understanding: The G6 sensor consists of contacts to the transmitter along with a set of wires (may be one loop) treated with chemicals of some sort that that keep the wire(s) operational (limit the natural decay due to exposure to interstitial fluid/blood). An electrical signal goes thru the wire, is affected by the glucose in the fluids, and the difference from a measured length of time it takes the signal to move thru the wire results in a particular BG reading. If the chemicals the wire are infused with are exposed for too long, it would seem a detriment to the lifespan of the wires capability to accurately indicate a BG level. Of course its possible the chemical(s) used don’t degrade to the point of non-usability for a measured amount of time significantly greater than the approve lifetime, so this shouldn’t be a factor (ergo those that restart sensors routinely are like the Energizer Bunny…up to a point!)
Just my brain’s interest in trivia and wanting to know how things work…I’ll also do some of my own research…
My research shows few articles actually tell you the mechanism of use for BG determination (apparently it falls under intellectual property secrets…understandable), but I did find this article at NIH: Continuous glucose monitoring devices: A brief presentation (Review) - PMC. that seems to be a decent guide, except its from 2021. Se la…it will have to do.
For me, the sensor adhesive does not last much longer than 10 days. So a pre-soak would definitely cut back on the days I could get out of a sensor.
Without any pre-soaking, I generally get 10 days. Sometimes I do a restart and get 11 days, maybe 12. But I don’t get much more than that.
@Tom, typically I “presoak” for around 12 hours and re-start a sensor once, getting 20 days of useful, active life. In a pinch (e.g., if I’m traveling) I will restart once more but likely not run out the full additional 10 days. The original Dexcom adhesive is usually peeling up after the first 10 days, so I’ll add an overpatch when I restart at day 11. This is definitely a YDMV situation!