Why Doesn't The Timer Work
The StrongLifts 5x5 app has a rest timer.
It tells you how long to rest between sets, and notifies you when you should do your next set.
If the timer doesn't work, check this:
1) Enable the timer in settings - timer.
2) Double-check notifications are enabled in your phone settings - notifications - StrongLifts. If nothing shows there, log a new workout, and then tap the first rep circle. A notification popup will show to enable it. If that doesn't work, reinstall the app and then immediately log a new workout and tap the first circle. This will trigger the notification popup.
3) Make sure you've enabled all notifications for StrongLIfts in your phone settings - notifications - StrongLifts. Every option must be enabled there for the timer to work properly.
4) Put your phone in ring mode and turn the volume all the way up. You will not get any notifications in silent mode obviously, and won't hear anything if the volume is low.