Bootcamp timer: run a class from one phone

Updated 6 November 2026

The rest of this guide covers how to choose the numbers, what to test the day before, and how to run the room.

Two trainers put the problem the same way. A poster on the StrongFirst forum wanted a timer mainly for use with clients because keeping training sessions within time constraints was something they struggled with. A trainer commenting on a Gymboss review wrote that stopwatches “require me to pay too much attention to the time and not enough to my clients.” The aim is to hand the clock to the phone.

Plan the class on paper first

Before you touch the timer, write the class as a short table. Start every class with a warm-up, and for beginners scale or swap high-impact moves such as burpees and sprints (step-backs and fast marching work); anyone with pain should stop. Decide:

• How long the main circuit is. Warm-up and cool-down come on top. One published boot camp routine, from the National Federation of Professional Trainers (NFPT), runs 50 minutes in total with a five-minute warm-up and a five-minute cool-down around the circuit.
• How many stations. Match it to your space, your equipment and how many people attend.
• Work and move time. Our circuit timing guide has a table by class length and station count. For a mixed group, 40 seconds of work and 20 seconds to move is a workable start.
• The break after each round. One to three minutes, for water and for you to explain the next round.

Here is a worked example. Eight stations, 40 seconds of work, 20 seconds to move, three rounds, three minutes between rounds. A round is 8 minutes. Three rounds are 24 minutes, and two 3-minute breaks make the circuit 30 minutes. With a 5-minute warm-up and 5-minute cool-down, the class is 40 minutes.

If you are choosing a work-to-rest ratio and are unsure, see the HIIT ratios guide. It covers what the research does and does not say about common ratios.

What the timer needs to do

For a class, check the timer against this list.

Need	Why it matters in a class
Repeats work and rest for a set number of rounds	The whole circuit is repeats
A different break after each round, or a longer break between sets	Round breaks are longer than station moves
Announces the next station	You can watch form instead of the clock
Counts down the last few seconds	People finish the interval together
Large numbers	A glance from a few steps away is enough
Keeps running with the screen locked	A pocket tap should not end the class
Shares the speaker with your music	You need both, from one phone

The built-in Clock app does not cover most of this. Apple’s guide describes it as a single countdown with an end sound, and we found no repeat or interval setting described for Google’s Clock app, so for a class you need an interval timer app. See how to set an interval timer on iPhone or Android.

Music and the speaker

Music matters in a class, and it is where one-phone setups fail most often. A timer that interrupts your music turns every station change into a gap of silence, or makes you switch the music back on mid-class.

Test it the day before: start your music from the app you will use, run a 5-second work and 5-second rest timer, and listen. The music should keep playing and the timer’s voice should be clear over it. Do it again with the screen locked. The music guide has the full 30-second test and explains why timers behave differently.

Then test the room: stand at the farthest station with the speaker where you will put it. If you cannot make out the cue, raise the speaker, turn the music down a notch, or choose spoken cues over beeps.

Calling the changes

The American Council on Exercise’s cueing article describes alerting cues as cues that tell participants about changes in movement or tempo before they happen, and gives the example of counting down to a recovery period during intervals. It also warns against excessive talking and recommends plain language. For a class that means:

• Let the timer say what is next and count the last seconds.
• Use your own voice for form, safety and encouragement, not for the clock.
• Say the easier and harder version of each station once, before the round starts, not at every station.

Mixed levels

Keep one clock. Give every station an easier and a harder version and let people choose, so no one is singled out. The circuit timing guide has an example table.

A day-before checklist

1. Phone charged, and plugged in or with a battery bank if the class is long.
2. Music app, speaker and timer tested together, screen locked.
3. Volume checked from the farthest station.
4. The workout saved in the timer so you can start it in one step, not typed in with a group waiting.
5. A backup: the plan on paper, and a stopwatch or second phone in your bag.

Running a class in Countcall

Countcall is built for this. You can save a class as a workout with named stations, with the voice saying the next station and the seconds, and very large numbers on the screen. Each round can have its own rest, and on Android, or on iPhone with iOS 17 or later, the timer stays on the lock screen. Your music keeps playing and, by default, dips while the voice speaks (a setting you can switch off); spoken audio such as podcasts pauses instead. With music playing, your earbuds’ button controls the music, so pause from the lock screen (on iOS 17 or later). The free version keeps two saved workouts and shows ads on a couple of screens, never during training; saving more takes a paid plan. The app is not in the stores yet; join the waitlist below and we will email you once when it is.