How to Set Up Multi-Phone Sprint Timing for Track Practice

A handheld stopwatch relies on human reaction at both the start and the finish. That introduces reaction-time error into every measurement. When a coach presses "go" and the athlete responds, the clock includes however long it took both humans to react — not just how fast the athlete ran.

True Elapsed Time

With a phone at the start line and another at the finish line, timing begins the moment the athlete's body crosses the start gate. The finish gate records the moment they cross the end. The difference is pure running time, with no reaction delay mixed in. This is the same principle used in professional Fully Automatic Timing (FAT) systems, scaled down to equipment you already own.

Split Timing

Multi-phone setups also unlock split timing. Place a third phone at an intermediate point -- the 20-meter mark, the halfway point of a 100-meter dash, or any distance that matters for your training plan -- and you get segment-by-segment breakdowns of acceleration, top speed, and deceleration. That data is far more actionable than a single finish time when you are trying to identify where an athlete gains or loses speed.

Step A: Position the phones

Place one phone at the start line and the other at the finish line. Each phone should be perpendicular to the lane the athlete will run through, with the camera pointing across the lane at approximately chest height. This ensures the detection system tracks the athlete's torso rather than an arm or leg, which matches how official timing works. If you are using tripods, extend them so the camera lens is roughly 1.0 to 1.3 meters off the ground. Position the phone about 1 to 2 meters back from the lane edge so the full lane width is visible in the frame.

Step B: Create a session on the host phone

Open TrackSpeed on the phone that will act as the host (either start or finish -- it does not matter which). Tap to create a new multi-phone session. The host phone will begin broadcasting its availability. On the second phone, open TrackSpeed and it will discover the host automatically. Tap to join the session. You will see both devices listed once they are connected.

Step C: Wait for clock synchronization

Once connected, the devices begin an NTP-style clock synchronization process. They exchange a series of timestamped messages to measure and correct for the clock offset between them. A sync indicator on each phone shows the current status. Wait until both devices show a successful sync before proceeding. This typically takes a few seconds and achieves sub-5-millisecond alignment.

Step D: Arm both gates

Tap the arm button on the host device and it will signal the other phone to arm as well. Both phones enter a ready state where the camera is actively analyzing frames for motion. The status indicator on each phone will show "Ready" once the gyroscope confirms the device is stable. If a phone is still wobbling from being placed on the tripod, give it a moment to settle -- the stability gate prevents false triggers from camera shake.

Step E: Run

The athlete takes their position and sprints. The start gate detects their body crossing the start line and records the timestamp. The finish gate detects the crossing at the finish line and records its timestamp. Because both clocks are synchronized, TrackSpeed subtracts the start time from the finish time to produce the true elapsed sprint time. The result appears on both phones immediately, along with a thumbnail frame of each crossing.

Split times reveal where in a sprint an athlete is fast and where they are losing time. A 100-meter dash might show a slow first 10 meters (acceleration phase) but a strong 60 to 80-meter segment (top speed). Without splits, that information is invisible.

Adding a Third Phone

To capture split times, place an additional phone at the intermediate distance you want to measure -- for example, at the 20-meter mark of a 40-yard dash, or at the 60-meter mark of a 100-meter sprint. Set it up the same way as the start and finish phones: perpendicular to the lane, chest height, stable mount. When the third phone joins the session, all three devices synchronize their clocks together.

Reading the Results

After the run, you will see the total time plus the time for each segment. For a three-gate setup at 0m, 20m, and 40m, you get a 0-20m split, a 20-40m split, and the total 0-40m time. Comparing these splits across sessions shows whether acceleration drills are paying off or whether an athlete needs to work on maintaining speed.

For specific guidance on timing a 40-yard dash with accurate phone-based timing, see our dedicated guide. It covers the particular distances and considerations for that test.

Timing Multiple Athletes Efficiently

You do not need to re-create the session between athletes. Once the gates are armed, each crossing is recorded as a separate run. Have athletes line up and go one at a time with enough spacing (10 to 15 seconds) between runners for the gates to reset. The session collects all runs in sequence, so a coach can time an entire team without touching the phones.

Keeping Phones Cool

Running the camera continuously generates heat, especially at higher frame rates. For long practice sessions, consider using 60fps instead of 120fps to reduce thermal load. If a phone starts feeling warm, pause the session and let it cool for a few minutes. Keeping phones out of direct sunlight helps too -- a small shade or placing the tripod so the phone faces away from the sun makes a noticeable difference on hot days.

Consistent Positioning

For comparable results across training sessions, mark where you place the tripods. Use tape on the track surface or note landmarks so you can reproduce the same setup next time. Consistent camera angle and distance from the lane means the detection triggers at the same relative position on the athlete's body, reducing variability in your data.

Combine multi-phone timing with structured sprint training drills to make the most of accurate timing data. Knowing exact split times lets you adjust rest intervals, distances, and training focus based on measured performance rather than guesswork.

The peer-to-peer connection between phones is generally reliable, but here are the most common issues and how to resolve them.

WiFi and Bluetooth Must Be Enabled

Even though you do not need a WiFi network, both WiFi and Bluetooth radios must be turned on. iOS uses them together to establish the peer-to-peer link. Check Settings or Control Center on both devices and make sure neither radio is disabled. Airplane mode will block the connection entirely.

Stay Within Range

The phones need to stay within approximately 30 feet (10 meters) of each other during the initial connection and clock synchronization. Once synced, the connection is more tolerant of distance, but for the most reliable operation keep them within reasonable range. For a 100-meter sprint, the phones will be far apart, which is fine -- the peer-to-peer protocol handles this well on open tracks without walls or interference. However, initial pairing works best at close range, so pair the devices before walking them out to their positions.

If the Connection Drops

If phones lose their connection mid-session, bring them back within range and the app will attempt to reconnect automatically. If it does not reconnect after 15 to 20 seconds, end the session on both phones and start a new one. The reconnection process is quick, and re-establishing the clock sync only takes a few seconds.

For persistent issues or questions not covered here, visit our support page for additional help.