Starting Loop: Compatible iPhone/iPod
The detailed list in LoopDocs is up-to-date and referenced by clicking on this link: Build App: Step 2: Compatible iPhone/iPod Touch. Be sure to read the whole page. Some information there is reinforced on this page along with some additional tips.
Important Fact: Loop is integrated with the Apple Health database.
Loop reads from and writes to that database, therefore, only an iPhone or iPod can be used with Loop. The iPad does not support Apple Health so you can’t Loop with it.
In addition to your primary Loop phone, a backup phone (see Have a Backup Plan) is recommended for Loopers (it does not need to be activated with a telephone number/mobile service).
There are alternate markets to purchase used cell phones (for example, https://swappa.com).
All looping phones should have an internal battery with a Maximum Capacity above 85% (look in Settings/Battery/Battery Health/Maximum Capacity).
Apple iOS and Mac OS and Xcode
When Apple releases a new phone operating system (iOS), a new version of Xcode is also released. Xcode is used to build apps for Apple Devices.
When a new iOS is released – wait until you get the all-clear from the Looping Community before updating your phone. That’s why you need to keep automatic update turned off on your phone.
Once you see reports that it’s ok to update your phone, it’s a good idea to update Xcode to a compatible version too, just in case you need to rebuild.
It is recommended that you practice rebuilding Loop at least once a quarter. This encourages you to keep your computer, Xcode and iPhone available to rebuild the Loop app if some new feature or safety concern is reported. For later reference, there’s a page on Version Updates that typically lists the most recent versions for iOS and Xcode along with instructions on how to stay up to date.