Apple Watch
Seconds for Apple Watch works independently of your iPhone. During workouts, Seconds will remain active in the background and provide haptic feedback to alert you of interval changes.
Interval Timer
Quick Intervals
The Quick Intervals editor lets you create simple HIIT, circuit and Tabata style timers quickly and easily.
You can adjust the values by tapping the buttons. Tapping and holding will continuously alter the value. The longer you hold the button the faster and bigger the value changes will become.
You may also change the values using the Digital Crown. Turning the Digital Crown slower will allow the finest value changes, whereas moving it quickly will result in bigger jumps.
Once you have defined your timer you will be take to the activity picker.
My Intervals
Although Seconds for Apple Watch works independently from your iPhone, the timers you create on the iPhone will still sync to the watch. Tapping on a timer will open the Activity Picker
Activity Picker
Seconds for Apple Watch needs an activity that it can provide Apple Health. If you have defined an activity within the timer editor on the iPhone you will skip this screen and take you directly to the timer.
The activity picker lets you choose a location and activity type you intend to perform while the timer is active. There values will affect the calorie expenditure the Apple Watch sends to Apple Health.
The activity picker will remember the last 5 activity/location combinations you have selected for quick access.
You tap the select whether you want an indoors or outdoors workout location. Tapping either again will remove the selection.
Selecting an activity will take you to the timer.
The Timer
While on the timer screen the app will be registering an active workout. This will prevent the app from being suspended when entering the background when you lower your wrist. It also allows the app to provide haptic feedback while the app is not on the screen.
The timer displays the current interval at the top of the screen and the next interval beneath it. The info bar at the bottom will display your current heart rate (assuming you have given Seconds permission to read it from the iOS app), the interval count, and the total time remaining.
Once your have ended a timer you have the option to restart it, or end your workout. Only ending the workout will prevent the app remaining active in the background.
Start and stop the timer
Tap on the current interval.
Advance to the next interval
Tap the next interval.
Scroll through the intervals
Rotate the digital crown. This will pause the timer.
End a timer
Force touch the screen and tap End Timer or Discard from the menu depending on whether you wish to save your current progress to Apple Health.
Reset the timer
Force touch the screen and tap Reset from the menu.
Summary
Depending on the permissions Seconds has been granted the summary provides details of workout length, calorie expenditure and heart rate information.
You have the option to save the workout to Apple Health or discard it. If your workout fails to save check you have granted Seconds permission to share workouts within the Apple Health app.
Apple Watch limitations
Apple Watch can only have one workout session at a time. Starting a new session will cancel any active sessions. Workout sessions are what allow workout apps to stay open in the background. Without a workout session, workout apps would become inactive and not able to do anything each time the user lowers their wrist.
From Apple's documentation:
Apple Watch runs one workout session at a time. If a second workout starts while your workout is running, your HKWorkoutSessionDelegate object receives an errorAnotherWorkoutSessionStarted error, and your session ends.
There is no way to get around this until Apple remove the limitations of Apple Watch.
Can't I use Seconds without a workout session?
Apple Watch apps are deactivated when the screen turns off and cannot do anything. In the case of Seconds this would mean the app would not be able to alert you of upcoming interval changes unless the app was actively on the screen. No one wants to exercise looking at their watch the entire time.