Smart referee flags, a keeper count, sin-bin and playing-time boards, and body cameras for referees and umpires
Software: No subscription required
Concept, not for sale yet. Tell us if you want it; that decides what we build.
Rate this idea and tell us what to change
Drag to rotate · right-drag to move · scroll to zoom · click a part for its size and placeSwipe to rotate · pinch to zoom · two fingers to move · tap a part for its size
How it fits together
Scroll or tap a part. Press “See the 3D CAD design” to watch the model, built from our CAD, light each part up and show how it connects.
Real-time 3D render · drag to rotate · final design may varySwipe sideways to rotate
01
The whole OffsideFlag
A smart assistant-referee flag senses a press, raise or wave and radios it to the referee's wrist unit, which buzzes and lights an LED.
02Brain
XIAO ESP32-C3 (flag grip)
The brain: it runs the flag grip firmware program
03
Motion sensor
Wakes the flag and detects a raise or a wave
XIAO ESP32-C3 (flag grip) · I²C (4 wires) · Acceleration, wake interrupt
04
Signal button
Gives a press signal with the thumb
XIAO ESP32-C3 (flag grip) · GPIO pin · Button press
05
Vibration motor
Buzzes the grip once to confirm the flag was heard
XIAO ESP32-C3 (flag grip) · GPIO pin · Motor on/off
06
Referee wrist unit
Buzzes and lights left or right LED for each flag
XIAO ESP32-C3 · ESP-NOW radio · 24-byte flag events
07
LineCam clip recorder
Saves 12 s of video around each flag
XIAO ESP32-C3 · ESP-NOW, then UART · Flag events
08
18650 cell
Powers the flag through a match
XIAO ESP32-C3 (flag grip) · Power lead via XIAO charger · 3.7 V power
09
QuarterBoard screen
Shows quarters played and who must start next
XIAO ESP32-C3 · ESP-NOW radio, then SPI · Quarter start and lineups
10
All connected
8 key parts, one program, and your phone
What it is
A pair of assistant referee flags with smart grips, a referee wrist unit and optional body cameras for referees and umpires.
What it does
Who it's for
Grassroots referees, baseball and softball umpires, referee associations and body-camera schemes.
How the parts connect
Every part, what links it to the brain, and how the data reaches your phone. A solid line is a cable; a dashed line is a radio link.
The program
for (;;) {
wait_for_wake(); // LIS3DH > 1.2 g or button (GPIO)
kind = classify(500); // press / raise / wave
msg = (flag_msg_t){ .ver = 1, .crew = crew_id, .flag = FLAG_ID,
.kind = kind, .seq = ++seq, .t_ms = now_ms() };
for (int i = 0; i < 3; i++) {
esp_now_send(BROADCAST, (uint8_t *)&msg, sizeof msg);
vTaskDelay(pdMS_TO_TICKS(20)); // receivers de-duplicate by seq
}
buzz(heard_beacon_last_10s() ? 1 : 2);
enter_sleep();
}To your phone
Referee's phone browser, after the match
One screen for each job OffsideFlag does.
Flag signalThe left assistant raises the flag behind the referee's back. The referee's wrist buzzes with a yellow light, and LineCam saves the clip.
Keeper countThe goalkeeper picks up the ball and holds on to it. The wrist unit counts the 8 seconds of Law 12 and buzzes when time is up.
Body cameraA player squares up to a lone referee, who says 'I'm recording' and presses REC. A red ring lights round the lens and the clip is sealed.
Sin binsA home player is sin-binned for dissent. The referee triple-presses the wrist, and the board on the halfway post counts down for both benches.
Everyone playsAt half-time a coach's third-quarter lineup leaves out #5, who sat the second. The board shows #5 MUST START and the referee warns the coach.
App screens with sample data. The interface is in development.
| Flag signal | Left flag: raise | Each flag |
|---|---|---|
| Event clip | 12 s MP4 | Each flag |
| Clip time | 18:02:11 | Each flag |
| Flag battery | 82% | With each event |
| Quarters played | #5: 1 of 3, must start Q3 | Each quarter |
Clips stay on the LineCam's own card until the referee opens the hotspot. No cloud upload.
CAD design · Rev A5 design complete (QuarterBoard 27 Oct 2026; SinBin A4, UmpCam A3, RefCam A2, KeeperCount A1), all hardware fit-checked in CAD, not built
| AI processor | Seeed XIAO ESP32C3 in each flag grip and the wrist unit; Raspberry Pi Zero 2 W plus XIAO ESP32C3 in each LineCam |
|---|---|
| Camera | Raspberry Pi Camera Module 3 Wide (102° HFOV, 2304 × 1296 at 56 fps), LineCam only |
| Sensors | Adafruit LIS3DH accelerometer in each grip · 12 mm IP67 thumb button · Coin vibration motors in grip and wrist unit · Guarded KeeperCount thumb button on the wrist unit · Guarded REC key and 3 red recording LEDs under a clear halo (RefCam) · SinBin board: 2.9 in e-paper with HOME and AWAY keys on the halfway flag post |
| Connectivity | ESP-NOW broadcast (no router needed) · Wi-Fi to the referee's phone for clip download (LineCam) or sealed upload to the county FA (RefCam) |
| Power | 18650 cell in each grip (charge monthly); 500 mAh LiPo in the wrist unit (about 2 matches); 2000 mAh LiPo in the LineCam or RefCam (about 3.9 h recording or 9 h armed, est.) |
| Enclosure | Black ASA grips (Ø36 × 231 mm) on 16 mm aluminium shafts; black ASA wrist unit on a 22 mm strap; white ASA LineCam with lens hood and GoPro-style mount |
| Dimensions | Wrist unit 52 × 38 × 13 mm; LineCam and RefCam 88 × 76 × 24 mm; SinBin board 120 × 62 × 30 mm |
| Weight | About 200 g per flag and 150 g per LineCam (est.) |
| Signal types | Press, held raise, wave |
|---|---|
| Flag to buzz | ≤ 150 ms (to be tested) |
| Range | ≥ 120 m across a full pitch (to be tested) |
| Crew isolation | Paired crew ID, no cross-triggers on nearby pitches |
| Count | 8 s, cue at 3 s to raise the hand |
|---|---|
| Timing accuracy | Within ±50 ms per count (to be tested) |
| Controls | Press to start or pause, hold to clear |
| Log | Each count with match time and result |
| Period | 10 min, 8 min or set per competition |
|---|---|
| Starts | At the restart press, not the card |
| Lost time and half-time | Paused with one hold on the wrist key |
| Battery | About 109 h, 40+ matches (est.) |
| Camera | Camera Module 3 Wide, 102°, 56 fps |
|---|---|
| Clip | 8 s before to 4 s after each flag |
| Detail across the pitch | About 8–49 mm per pixel at 10–64 m |
| Runtime | About 3.9 h per charge (est.) |
| Starts recording | Only on REC key or wrist double-press |
|---|---|
| Warning | Red ring round the lens, 3 s blink then steady |
| Clips | Encrypted to the county FA's key; deleted after upload or at 60 days |
| Battery | About 3.9 h recording or 9 h armed (est.) |
| Flag grip | Months on standby; charge monthly |
|---|---|
| Wrist unit | About 4.5 h, 2 matches |
Targets for production units; they may change during development.
Hardware: $99–$599 per SinBin board, QuarterBoard, LineCam, Set or Crew Kit
Software: No subscription required
Target prices: $249 OffsideFlag Set (2 flags and wrist unit), $99 SinBin board, $119 QuarterBoard, $199 per LineCam, RefCam or UmpCam, $599 Crew Kit. Parts cost at quantity 1 is about $96 per Set, $52.28 per SinBin board, $61.58 per QuarterBoard, $120 per LineCam, $121 per RefCam and $337 per Crew Kit (est.).
$249 (target)
Two smart flags and a referee wrist unit.
$99 (target)
Sin-bin board for the halfway flag post, run from the wrist unit.
$119 (target)
Playing-time board for youth leagues, under the SinBin board.
$199 (target)
Chest body camera for a referee without assistants, for county FA and league schemes.
$199 (target)
Optional chest camera for one assistant referee.
$599 (target)
A Set plus two LineCams for a full crew.
Indicative launch pricing in USD, excluding taxes and shipping. Final pricing is confirmed before any balance is charged.
Community
OffsideFlag is in development. Rate the idea, tell us what to change about the features, specs or price, and we'll build it with your feedback.
How much people want it
–
No ratings yet
Follow OffsideFlag
Get build updates and first access when pre-orders open.
No comments yet. Tell us what you'd want from OffsideFlag.
Questions
Tell us what this would save you, or ask anything. We reply within two business days.
A member of the IEMI Labs team will reply within two business days.
From the product lab · ideation phase
No. OffsideFlag is a concept in the in-house design and testing stage. It is designed and fit-checked in CAD but has not been built, and range, latency and battery figures are targets.
No. The buzz only gets the referee's attention, as IFAB guidance describes for beep flags. The LineCam shows what the assistant saw from where they stood. It is not VAR and is not approved by FIFA or IFAB.
Triple-press the wrist key when you send the player off, then press once as play restarts: the period starts then, not when the card was shown. Hold the key for 2 seconds to pause every sin bin for an injury or other stoppage, and again to restart; at half-time the remaining time waits for the second half. The board on the halfway flag post shows HOME or AWAY with minutes left, and the wrist buzzes twice when a period is served.
No. The board only shows READY. As the FA and IFAB guidance says, the player waits on the touchline until the ball is out of play and the referee gives permission. The referee is still in charge of time, and a second sin bin or caution is still the referee's call.
Flag posts at the halfway line are allowed under Law 1, at least 1 m outside the touchline, and must carry no advertising, so the board has no logo on the pitch side and straps to the post. Sin bins themselves only apply where the competition uses them; where it names a team official to keep the time, both benches can now see it.
Only when the referee presses the REC key or double-presses the wrist key, after telling the players. A red ring round the lens blinks for 3 seconds and then glows while it records. There is no hidden recording, and no pre-roll unless the competition's own rules allow a short one.
Only the county FA or league that runs the scheme. Each clip is encrypted to their key with a time and hash log, so the referee and the clubs cannot watch, edit or post it, and the card copy is deleted after upload or at 60 days.
Body cameras are a competition option backed by IFAB after the FA's grassroots trial, not standard equipment. RefCam is for schemes a county FA or league runs. It records conduct for disciplinary cases and never changes a match decision.
Yes, as UmpCam: the RefCam on a clip that drops over the umpire's belt next to the ball bags, because the plate umpire's chest protector is under the shirt. It records only when the umpire presses REC, never reviews a call (judgment calls are final), keeps audio off because Little League bars microphones on umpires, and is used only where the league or tournament allows it, shown to both managers at the plate meeting.
Holding REC for 2 seconds marks the clip as an ejection. After the game the phone app opens a report draft with the date, field, clip time and a fingerprint of the clip; the umpire adds the inning, who and why, and the app counts down the 24-hour (or 48-hour) deadline and sends it only to the assignor or tournament director.
An assistant's LineCam keeps a 20-second ring in memory that is overwritten all the time. A clip is saved only on a flag event or a long press, and clips stay on the LineCam and the referee's phone.
No. The referee still judges when the keeper has the chance to release the ball and presses the button then, and still shows the last five on a raised hand. The wrist unit only keeps the count the same length every time and logs it.
The flags can. The LineCam ships disabled for youth matches, because filming children is tightly controlled; it stays adult-only until a league or county FA approves it.
Each competition must allow electronic flags and body cameras. We plan to ask one adult league to permit a trial season before any wider use.
No. It counts the quarters each player started and warns early. The referee still warns the coach and reports a coach who refuses, and the league decides any penalty. It never stops play or blocks a substitution.
You set it per league: AYSO National's half a game, Region 76's three quarters, keeper limits by age, and late arrivals (after the 2nd quarter starts a player is owed one quarter). Credit goes to the player who starts the quarter, as AYSO counts it.
IEMI's one cricket product: a smart wicket pair at Law 8 size, with every sensor inside the stumps.
From $1,990 per CricketOne
Details
IEMI's one football product: a pair of legal full-size goals with cameras, computers, batteries and radios inside the posts and crossbar, and a referee wrist unit.
From $4,690 per pair of smart goals with sockets and the referee wrist unit
Details
IEMI's one basketball product: the backboard, ring, padding and shot clock at both ends of a court, with a camera, a computer, a rim sensor and edge lights built in, and one app.
From $4,990 per court: two smart backboards with rings, padding and shot clocks
DetailsOffsideFlag
Concept · target $99