BeastieThe jumping jack counter
that wants both halves
A jumping jack is two movements pretending to be one. Beastie watches both through the phone camera — your feet splitting and your hands going overhead — and banks a rep only when both actually happened. Tired arms at shoulder height are called out, not counted.
If it’s not sure, it doesn’t count.
iPhone & Android · free solo counter · no account needed to try it
The rep that quietly shrinks.
Nobody sets out to cheat a jumping jack. It just gets smaller as the set goes on — the arms stop short first, then the feet. The camera holds the shape steady for you.
Feet apart and hands up
The rep banks when your ankles have separated and your hands have cleared your head, then you close back up. One without the other is half a jumping jack, and half a jumping jack is not a jumping jack.
One side can’t carry the other
When one half of the body starts lagging — a lazy left arm, a foot that stops committing — the overlay flags it mid-set, while there is still something you can do about it.
Nothing to tap, nothing to wear
Prop the phone up, step back, go. Framing is checked before the set starts, the count is huge and spoken out loud, and nothing needs charging on your wrist first.
A wrist only ever sees one arm.
Jumping jacks are the exercise a wrist tracker is worst at. It feels one arm swinging and infers the rest, which is why a vigorous wave can run up a count. A camera looks at the whole body at once, so the thing being counted is the thing you actually did — both halves of the movement, every time. That is the same reason Beastie can referee a duel: the counting runs on each phone, and neither player is trusting the other one to be honest.
Solo counts. Duels settle.
On a quiet day it’s an honest solo counter — your jumping jack PR and your streak move, and streaks pause rather than break when life happens. When you want stakes, call someone out: pick jumping jacks, set a number, send the link. They don’t need an account to accept, and both phones referee their own side. Beastie counts push-ups and squats the same way — three moves, counted properly, with more coming as they pass the same bar.
Before your first set
How does a jumping jack counter work without a wearable?
Beastie tracks points on your body through the phone camera, on the phone itself. A jumping jack is two movements at once, so it watches both: your ankles separating and your hands rising above your head. When both have happened and you close back up, the rep banks. A wrist tracker only ever sees one arm, which is why it can be fooled by waving.
Do half-hearted jumping jacks count?
No. Feet that barely part, or arms that stop at shoulder height, leave the rep unfinished and it doesn’t go on the board. You’ll see the limbs flag orange while the set is still running, so you can fix it rather than find out at the end.
Where do I put the phone for jumping jacks?
Facing you, propped about knee height, and further back than you think — jumping jacks are the widest of the three exercises, so your hands at full stretch and your feet at full split both need to stay in shot. Beastie checks your framing before the set starts and won’t count until it can see all of you.
Can I challenge a friend to jumping jacks?
Yes. Pick jumping jacks, set a number and send the link. Your friend doesn’t need an account to accept, and both phones referee their own side, so neither of you is trusting the other’s counting.
Does the video go anywhere?
No. The pose detection runs entirely on your phone and frames are discarded as they are analysed — nothing is uploaded and nothing is stored. It counts in airplane mode, which is the simplest proof of it.
Beastie is a general fitness product, not medical advice. Form feedback is about scoring reps fairly, not a health assessment.
Both halves, or it doesn’t count.
Do one set and see how many survive a counter that wants the feet and the hands. It takes about a minute, and it settles the question of whether you were ever really doing them properly.
- Free — no card, no trial to cancel
- No account needed to try it
- Video never leaves your phone
- Counts with no signal
your phone
One set takes about a minute. If the number disappoints you, nobody else ever sees it.
Every rep, earned.
The video never leaves your phone — counting runs on the device, even in airplane mode. Wondering what a good number is? See how many jumping jacks people do in a minute.