It tells you which kid to sub before the heat does.
A box on the sideline reads the heat on your field, and every player wears a band. When one kid is getting into heat trouble, the box buzzes and shows their number. When they've recovered, it tells you that too. You don't need an app, and there's nothing to set up.
What the weather app doesn't tell you
Your weather app is reading an airport.
Field conditions can run several degrees hotter than the nearest station.
⚠ SOURCE NEEDED · field vs. station temperatureThe rule says check WBGT every 30 minutes. Nobody does.
A Kestrel meter needs someone standing there to read it, and most youth teams don't have an athletic trainer.
⚠ SOURCE NEEDED · link the 30-minute guidelineWeather isn't the player.
The kid who sprinted for 20 straight minutes and the kid on the bench are in very different places.
How a hot Saturday plays out
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1 · the box
Set it on the sideline. It reads heat, humidity, sun and wind right there on the field.
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2 · the band
Players wear a band. It knows when they're on the field, how hard they're going, and when they're resting.
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3 · it tells you who
#4 has been sprinting in the sun. When their heat load crosses the line, the box buzzes and shows their number. The band buzzes too.
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4 · it tells you when
Once #4 has cooled down and recovered, the box shows OK TO GO, so you don't have to guess how long to keep them out.
No app. No pairing. No Wi-Fi. Turn it on.
The questions you're already asking
"Is it safe to keep going today?"
Live field WBGT with the flag levels athletic trainers already use. · in the box
"Who needs a break right now?"
A heat-strain score for each player, built from field heat plus that player's effort, heart rate, oxygen and body temperature. You see one thing: #4 SUB NOW · in the box
"Can they go back in yet?"
#4 OK TO GO once that player has recovered. · in the box
"Are my players ready for the heat yet?"
Heat acclimatization progress for each player through preseason. PRO
"Who's gassed?"
A fatigue level for each player (fresh, tiring or gassed), worked out from effort and recovery. You won't see heart-rate or oxygen numbers. PRO
"Who actually worked hardest today?"
Workload score, sprint count and hard stops. PRO
"Are we working as hard in practice as in games?"
Effort trends, game vs. practice. PRO
"Did I rotate the bench fairly?"
On-field and bench time for every player, tracked automatically. PRO
Safety is never behind the paywall.
Every team that buys the box gets the full heat alert, with nothing to set up. The app adds coaching stats on top. It never holds back a safety feature.
Sentry Pro
⚠ NAME TBDPro shows coaching stats. It doesn't show health data: heart rate, oxygen and temperature never appear as numbers, and they only feed into scores like the fatigue level.
Heat acclimatization
lead featureHeat-safety guidelines (KSI, NFHS) call for roughly 14 days of gradual heat acclimatization in preseason. Pro shows where each player is in that process, like "day 9, adapting well" or "behind the team", by tracking how their body's heat response improves from one day to the next.
⚠ CITE the specific KSI / NFHS guidelineFatigue level
Fresh, tiring or gassed, worked out from effort and recovery. It answers "who's gassed?" without showing a medical reading.
Minutes on field vs. bench
The band works this out from movement, so nobody has to keep a clipboard.
Workload score
How much work a player actually did, counting movement as well as minutes. Two kids can play the same minutes and do very different amounts of work.
Sprints & hard stops
Bursts of speed and sharp decelerations. Hard stops are where hamstrings and ACLs take the most stress.
Jumps
For basketball and volleyball: how many, and how hard the takeoff was.
Work-to-rest
Load per active minute, and how quickly a player's movement bounces back after a burst.
Game vs. practice
Whether practice is as intense as games, tracked across the season.
Price
⚠ PRICE TBDYour players' data: who sees what
Health readings
Heart rate, oxygen, temperature and motion feed the heat alert. Nobody sees them as numbers.
The alert
#4 SUB NOW, #4 OK TO GO and the field's flag level.
Coaching stats
Minutes, effort and scores worked out from them, like the fatigue level. Pro never shows the readings themselves.
Why not just buy something else?
| Option | Field heat | Per player | Live alert | No app | Price |
|---|---|---|---|---|---|
| Handheld WBGT meter Kestrel | ✓ manual | no | no | ✓ | ~$400 |
| District weather systems Perry Weather | ✓ | no | siren | no | district budget |
| Industrial heat wearables Slate Safety, Kenzen | no | ✓ | ✓ | no | ~$800 / band |
| Pro GPS trackers Catapult, STATSports | no | ✓ | no | no | pro budget |
| Sideline Sentry | ✓ | ✓ | ✓ | ✓ base kit | ⚠ TARGET PRICE |
What's in the bag
The sideline box
It reads heat, humidity, sun and wind on your field, shows the flag level and the alert, and buzzes when it needs you.
The band
It reads heart rate, oxygen, temperature and motion, and all of it goes into the heat alert. It buzzes when its player needs to come off.
Heat log
The box logs every alert and flag change, so your league has a record.
⚠ EXPORT WITHOUT THE APP: USB / SD / PRINTOUT?Kit price
⚠ PRICE TBDWhy we're building it
Pilot it with your team.
We're looking for coaches, athletic trainers and league admins to run Sentry at real practices and tell us what's wrong with it. The form takes about two minutes.
Thanks, coach.
Toby reads every one of these and will email you himself at . You won't end up on a mailing list, and nobody will try to sell you anything.
You said you're up for a 15-minute call. He'll send a couple of times that work.