How does a two-phone sprint timing app work?
One iPhone is the Start phone and plays the start sequence. A second iPhone is the Finish phone and watches a defined finish line through its camera. The devices pair into the same session and synchronise before a repetition. Once the finish camera is actually ready, the Start phone can run the sequence and the Finish phone reports a detected crossing.
The aim is a useful training time from the start signal to camera detection, with minimal equipment: two supported phones and stable placement for the finish camera. It is not a claim of certified photo-finish equipment or an official race result.
More than a starter: practical training examples
Use the phones you already own. Photo Finish is being developed for athletes who want to time repetitions and coaches who want a finish-camera training result without buying a dedicated timing kit. You still need two supported iPhones, the applicable app access and a secure mount or stable support. Photo Finish remains a private beta; its price and public release date are not final.
- Solo athlete, 10–30 m acceleration: place the Start phone where you can hear the signal; mount the Finish phone side-on at the measured end point. Connect, prepare and arm the camera, return to the start, then run through the line. Check the detected time and crossing frames before repeating.
- Coach or field-sport athlete, 20–40 m speed repetitions: use the same start position and finish-line placement each time. The current app gives an athletics start sequence; this is a training setup for another athlete group, not a released football or agility protocol.
- 60 m or 100 m practice: first test a hotspot setup across the entire intended separation. Start-phone hotspots and a third phone’s hotspot have extended coverage in field tests, but a 100 m connection is not guaranteed. A hotspot phone in the middle is a network access point, not a RaceCue split timer.
- Coach supervising several finishers: V2’s optional group mode keeps capture open for successive crossings until a phone operator ends it. Allow a clear gap and review the candidates; closely overlapping runners can merge. This is an additional experiment within the private beta.
These times run from the app’s GO to a detected finish-line crossing. They include the athlete’s response to GO; they are not a flying-sprint split or movement-to-finish time. Measure the distance yourself. Keep the same measurement method when comparing repetitions.
Prepare a stable finish camera
Mount the Finish phone securely with a clear, side-on view of the finish. Keep the finish line in the image and the camera fixed. Calibrate an empty scene, then check the readiness message before starting a run. The Start phone must receive the Finish phone’s ready state; a local camera preview alone does not prove that the pair is ready.
The private build includes remote preparation and optional automatic re-arming. Automatic re-arming waits for a clear, still view that matches the accepted scene. It prepares the next repetition; it does not start another race. If the Start timer is still running, finish or reset that repetition first.
Why choose a smaller detection area?
A full-image detector can respond to movement that is unrelated to the athlete: a nearby arm, a spectator or changing background detail. RaceCue’s test build includes a middle detection zone and a custom rectangular selection over the finish-line segment. Position the selection at the height that fits the intended drill.
A torso-height zone may help reduce triggers from movement above or below it. It does not identify a chest automatically or guarantee that an arm inside the selection will be ignored. A lighting filter and sensitivity controls are being tested for changing outdoor conditions, but a stable scene and deliberate placement still matter.
Will the phones connect across a sprint distance?
Keep Wi-Fi and Bluetooth enabled on both phones. A direct outdoor setup does not require a home Wi-Fi network or internet connection. For a hotspot setup, connect the relevant phones to that hotspot and confirm the RaceCue synchronization and camera-ready messages before moving to full distance.
| Connection setup | Reported separation | How to use it |
|---|---|---|
| Two phones, no shared Wi-Fi network | About 40–50 m | Start with short accelerations; test the actual track and placement. |
| Start phone’s Personal Hotspot; Finish phone joins | About 70–80 m | Confirm the Finish phone stays on that hotspot across the intended distance. |
| Third phone’s hotspot near the middle; both timing phones join | About 120–150 m in limited tests | Preliminary longer-range option; the middle phone runs the hotspot, not a split-timing app. |
Results vary with phone models, network routing, surroundings, battery/power settings and placement. These tests do not isolate the cause of any later connection loss. A connection at one distance does not establish timing accuracy. Check synchronization, camera readiness and repeated operation at the full separation before relying on the setup. Keep both apps visible and the Finish camera fixed.
With both phones on the same local Wi-Fi network, a wider testing area may be possible while both remain in coverage. Network isolation or blocked local discovery can still prevent connection. This is a setup option to test, not a measured range promise. See the shared Wi-Fi diagram. A separate one-phone + Bluetooth speaker PF scenario is also entering private testing, with a walking delay and automatic start. It uses a local audio-cue reference rather than the synchronized timing-phone pair, and Bluetooth output delay still needs validation.
If the link is lost, a repetition must not quietly become a valid finish time. Reconnect, confirm synchronization and camera readiness, then start a fresh repetition. The current private beta supports two iPhones only. Android-to-Android comes next for validation, followed by a separate mixed iPhone/Android trial; neither is available in the current PF beta.
How to test: choose your connection setup
Standard private PF workflow: two timing iPhones. PF timing messages use local Wi-Fi; Bluetooth alone does not carry the PF link. Keep both radios enabled for a consistent setup. Android-to-Android is planned after iPhone validation, followed by mixed iPhone/Android testing. A hotspot device supplies a network; that does not make it a supported Android timing phone.
1 · Direct nearby phones
About 40–50 m reported · test observation, not guaranteed coverage
Two iPhones connect directly; no shared router or hotspot. Keep Wi-Fi and Bluetooth enabled.
- Choose Start phone on one iPhone and Finish phone on the other; join the same RaceCue session code.
- Start nearby. Prepare and arm the Finish camera, then test a complete crossing.
- Increase separation gradually. Check synchronization and camera readiness again at the actual distance.
2 · Start phone is the hotspot
About 70–80 m reported · test observation, not guaranteed coverage
The Start iPhone shares its Personal Hotspot. The Finish iPhone joins that hotspot.
- Enable Personal Hotspot on the Start iPhone; join it in the Finish iPhone’s Wi-Fi settings.
- Open RaceCue on both phones, choose roles and the same session code, and wait for synchronization.
- Prepare and arm the Finish camera. Test at full separation before running your session; verify the Finish phone stays on the hotspot.
3 · Third phone provides the network
About 120–150 m in limited tests · test observation, not guaranteed coverage
Both timing iPhones join a third phone’s hotspot near the middle. The middle phone supplies Wi-Fi only.
- Place a third hotspot-capable phone near the middle of the intended phone-to-phone distance and enable its hotspot.
- Join that hotspot from BOTH timing iPhones. The middle phone is not a RaceCue split timer and does not collect a third finish.
- Connect the two RaceCue roles, confirm synchronization, prepare and arm the Finish camera, then test several complete runs at full distance.
4 · Two phones on the same Wi-Fi network
Coverage depends on the network · test option · setup option, not a measured range claim
Both timing iPhones join the same local Wi-Fi network, such as a sports hall or track access point. This can support a wider testing area than a direct nearby link if the network covers both positions and lets the phones communicate.
- Join the same local network on both timing phones. Internet access alone is not enough: guest/client isolation, different subnets or blocked device discovery can prevent joining.
- Create/join the same RaceCue session code nearby, then place both phones inside Wi-Fi coverage. Leave Wi-Fi and Bluetooth enabled; the PF timing data uses the local Wi-Fi connection.
- Prepare and arm the Finish camera. Test repeated complete crossings at the intended separation, and recheck synchronization after moving or roaming between access points. No longer-distance result is guaranteed.
5 · One finish phone + Bluetooth speaker
Single-phone PF experiment · private testing, not publicly available
The experimental workflow is one fixed iPhone giving the starter cue and monitoring the finish line, with a speaker near the athlete for audibility. Choose One iPhone in the beta setup helper, prepare and arm the finish camera, then schedule an automatic Marks–Set–gun or 3–2–1–GO start. This is a different mode from the existing two-phone synchronized PF workflow.
Bluetooth speakers have variable output delay and range. A timer started when the phone issues a cue may not match when the speaker plays it. If using the finish phone’s own speaker instead, sound travelling 60 m takes roughly 0.18 seconds in normal air conditions. The start reference must be explained and validated before comparing these results with other methods.
Training alone: set “Walk to blocks time” long enough to walk back to the blocks before the automatic sequence begins. The finish phone must stay fixed, awake and in RaceCue. With a helper: they can schedule the start with no walking delay once you are ready. Only one finisher is supported in this experiment; no Watch or split integration. The speaker is not a timing gate, split station or Wi-Fi extender. The public app can already play start cues through a speaker with a manually stopped timer; automatic single-phone PF is still private testing.
Use the same short check before every track session
- Prepare: matching beta versions on both iPhones, sufficient battery, Wi-Fi and Bluetooth on, required local-network/camera permissions allowed, both apps visible. Start with the phones nearby.
- Place: mount the Finish phone side-on, align the green line with your measured finish, and place the custom box across that line at the height you want monitored. The box limits the monitored line segment; entering the box alone is not the finish.
- Choose: One person is the default. Multiple finishers is a separate V2 option; keep it phone-controlled and allow a clear gap between crossings.
- Arm: Prepare camera on the Finish phone, keep the line clear, then Arm finish line. Confirm the Start phone sees readiness. Start can request remote preparation after initial setup; optional re-arm only prepares another repetition.
- Test: run three to five short trials, inspect the measured time and crossing frames, then repeat at the full intended separation. A connected badge alone does not validate a finish or establish accuracy.
- Recover: if disconnected, reconnect and confirm fresh synchronization and camera readiness before a new run. An interrupted run must not be treated as a valid finish. If a third hotspot is used, check both timing phones are still joined to it.
Keep supports out of the running path. The reported ranges describe phone-to-phone separation, which can differ from running distance when phones are offset from the track. Battery, background activity and radio conditions can affect a session, but the existing tests do not isolate those causes. A third hotspot is a possible coverage enhancement, not guaranteed 100 m support.
How does this compare with buying timing equipment?
The attraction is avoiding another dedicated timing purchase when you already have suitable phones. Equipment does not all cost thousands: sensor-and-app products can be cheaper than complete gate systems. This snapshot is for context, not a claim that camera training estimates match dedicated gate performance.
- Cronox’s manufacturer store lists its 2.0 timing system at €329.99 and wireless 3.0 at €493.28.
- OVR Sprint’s two-gate Starter Kit is listed at US$529.
- Freelap Sprint Pack 1 at UK retailer Athletics Direct is listed at £690.41 including VAT (£575.34 before VAT).
- JAWKU Speed’s wearable sensor product is listed at US$159.99 on its product page; it is a different sensor-and-app setup, with app subscription products also listed.
Prices checked 18 October 2026; promotions, included components, stock, shipping, taxes and app terms vary. These are examples found in a limited survey, not the cheapest products worldwide. RaceCue PF needs two phones and stable camera placement, remains in testing and has no final public price. Dedicated gates have different start methods, sensing and operating requirements; do not compare GO-to-finish times directly with movement-triggered gate times.
Can watch reaction and camera finish be combined?
In the one-person private workflow, a supported Watch provides optional wrist-reaction feedback while the finish camera supplies the run’s elapsed time. The accepted camera finish stops the Start phone timer and is sent to the Watch; if the Watch is out of range it may receive that result later. The Watch’s PF abort control cancels a one-person run without saving a finish time.
Group mode is phone-controlled in the latest private candidate: one runner’s Watch must not stop everyone’s capture. Start and end group capture on a phone. Wrist reaction is not measured for the group. The public Apple Watch release does not include Photo Finish. Explore the public Apple Watch features.
Multiple finishers: a separate V2 experiment
One person is the default. When both phones run a compatible V2 test build, the Finish operator can select Multiple finishers and optional silent review video. After each crossing, clear the monitored line and wait for Ready for finisher 2, 3 and so on. End capture on either phone when the group has finished.
Review the numbered candidate times and crossing stills. Up to 20 crossing candidates can be captured, while each phone’s recent history keeps the newest 10 entries. The optional local video lasts up to two minutes; save it on the Finish phone before leaving or recording another capture. Video review does not automatically identify athletes or generate missed crossing times.
When will RaceCue Photo Finish be released?
There is no public release date or final Photo Finish price yet. Apple Watch is publicly available for iPhone. Photo Finish reliability is the current testing priority; Android finish timing, mixed-phone timing and hosted multi-phone reaction challenges remain later roadmap steps. Follow RaceCue’s updates for test progress and release announcements.
In the meantime, the public sprint-start app offers realistic start commands, voices, pressure settings, camera start tools and session practice. For training ideas, see how to practise sprint starts and the reaction-time training guide.