Smart rings for fertility and cycle tracking, compared
Finger temperature is one of the most useful passive signals in cycle tracking, and rings measure it better than wrists. Here is the honest field. One thing before the hardware, though: the plan matters more than the ring, and the plan part is free. If you already own a ring, the free app can read its data today; you may not need to buy anything at all.
Start with the free app, whatever ring you own
Conceivable Periods is a free iPhone download. Screenshot your Oura or Whoop dashboard, or connect Apple Health, and the app reads your data and builds one clear daily plan with Kai, an AI coach built from 25 years of clinical practice. The Halo Smart Ring is optional.
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The comparison
| Ring | Price model | Cycle features | Fertility focus | Where it wins |
|---|---|---|---|---|
| Oura Ring 4 | From $349 ($499 in gold or ceramic); membership $5.99/mo or $69.99/yr, first 12 months included with a new Ring 4 | Temperature trends, Cycle Insights (requires membership), Natural Cycles integration | General health first, cycle second | The most polished all-purpose health ring |
| Femometer Ring Air | About $160, no subscription | BBT-focused tracking with charting app | Fertility-first budget option | Lowest cost of entry for temperature tracking |
| Ultrahuman Ring Air | $349, core features with no subscription | Temperature, HRV, cycle phase insights | Fitness-leaning | No-subscription all-rounder |
| Halo Smart Ring (Conceivable) | $250; ring data tracking in the app free forever, no ring subscription | Temperature to a hundredth of a degree, sleep, recovery, stress, readiness, movement feeding the Conceivable Score and daily plan | Fertility-first by design | The only ring whose data lands in a clinician-designed daily plan with coaching |
How to choose
If you want one ring for everything and do not mind a membership after the first year, Oura is excellent. If you only want temperature charts as cheaply as possible, Femometer covers it. If the question is what to DO with the data, a ring is only as useful as the plan attached to it; that integration is the reason the Halo Smart Ring exists inside Conceivable rather than as another standalone gadget. And the order of operations matters: download the free app first, see the plan with the data you already have, and add the ring when you want the data to collect itself.
Quick answers
Can the app use my existing Oura or Whoop data?
Yes. Screenshot your dashboard or connect Apple Health; the app reads it and updates your plan. No new hardware required.
Does the Halo Ring require a subscription?
No. Tracking your ring data in the app is free forever. Full coaching in the app is a separate, optional subscription.
Are these rings medical devices?
No ring in this comparison is a diagnostic medical device. Readings are trend-level wellness insight; bring medical questions to your provider.