This feature is awesome! I told the Dexcom tech support team about this a long time ago and they didn’t believe me. Had them pull up my profile information and I walked them through it. Surprised them that their product worked like this.
A couple days ago I found that G6 works in a somewhat similar way but with one BIG caveat. When you install a new sensor before the previous one ends (and put the already registered transmitter in) you get readings immediately. Their app doesn’t seem to require the 4 digit sensor code to work a new sensor as it defaults to any time left on the previous sensor - basically overriding the two hour warm up. However, this is the caveat…. When the 10day usability period from the previous sensor ends it will end the new sensor readings. When you click the “start sensor” button it will start the 2 hour warmup clock and after a while it will stop the warmup and claim you can’t restart the new sensor and must enter a new sensor. Basically, DON’T do this even if though their own app seems to support it at first. I will say that the instantaneous readings I got with zero warmup were 98% accurate as I did a blood test to check it.