I think that's how the Libre 2 works, when I tested it a couple of months ago I set the alarms at 80 and 160 and as long as the phone was near the sensor i.e. in my pocket or in the same room it pinged me as it got to those numbers.
I just had the rep from Ypso MyLife pump here today and had a good conversation with him about their system with the Dexcom G6 which is just about to start delivery, in March the will have the app connected to the pump but only one way coms from the pump to the phone but in May they will send out a new pump that has 2 way coms and you will be able to bolus from your phone. beginning of next year they will upgrade the software again to make it a closed loop system.
I have the Tandem Tslim rep coming next then I will decide which way to go, I sort of like the idea of that on because the IQ software can give a bolus on its own if you start to go high so we will see what they say next week, of course I'll post what I hear.