Our pick
Tempdrop for accuracy and value. Ava if you want multi-metric tracking. Femometer Ring if you want the lowest price point and don't mind a ring form factor.
What These Devices Actually Do
All three wearables track your basal body temperature (BBT) continuously while you sleep. After ovulation, progesterone causes a slight temperature rise (0.3-0.5°F) that confirms ovulation occurred. By tracking this pattern over multiple cycles, the devices learn your personal rhythm and predict your fertile window.
The key advantage over a regular oral thermometer: you don't need to take your temperature at the exact same time every morning. The wearable collects data all night and uses algorithms to filter out disturbances (getting up to pee, tossing and turning, room temperature changes).
Head-to-Head Comparison
| Feature | Tempdrop | Ava Bracelet | Femometer Ring |
|---|---|---|---|
| Price | ~$189 | ~$299 | ~$99 |
| Wear location | Upper arm (armband) | Wrist (bracelet) | Finger (ring) |
| What it tracks | BBT only (but very accurately) | BBT + pulse rate + breathing + HRV + perfusion + skin temp (9 parameters) | BBT + sleep quality |
| Ovulation detection | Peer-reviewed: 99% fertile window, 93% ovulation day | Zurich study: 89% accuracy for 5.3 fertile days | No peer-reviewed accuracy data |
| App quality | Good. Charts, CM tracking, cycle forecasts. Premium tier adds fertile window predictions | Polished. Multi-metric dashboard. Pregnancy mode after conception | Basic. BBT chart + period tracking. Clean but simple |
| Comfort | Lightweight armband. Most users forget it's there. Adjustable strap | Wrist bracelet. Some users find strap uncomfortable or sweaty. Vibrating alarm | Slim ring. Comfortable if sized correctly. May feel bulky for small fingers |
| Battery | Coin cell, lasts ~1 year | Rechargeable, ~12 hours per charge | Rechargeable, ~4 days per charge |
| Best for | Accuracy-focused trackers, FAM users, irregular sleepers | Data enthusiasts who want the full biometric picture | Budget-conscious, first-time trackers |
| PCOS/PMOS friendly? | Yes — works with irregular cycles | Not recommended for very irregular cycles | Limited data for irregular cycles |
🏆 Our Pick: Tempdrop
Tempdrop wins on what matters most: accuracy. A peer-reviewed study found it identifies the fertile window 99% of the time and pinpoints ovulation day in 93% of cycles — outperforming both wrist and ring wearables. It works for irregular sleepers (shift workers, parents of young kids) because its algorithm filters out disturbances rather than requiring consistent sleep patterns. And at $189, it's $110 cheaper than Ava.
The trade-off: Tempdrop tracks BBT only, not multi-metric data. If you want heart rate variability and breathing patterns, Ava offers that. But for most TTC purposes, accurate BBT is what matters.
Ava Bracelet
Ava's appeal is breadth — it tracks 9 physiological parameters and presents them in a polished dashboard. The vibrating alarm is gentle, and the pregnancy mode is a nice touch once you conceive. But accuracy matters more than data quantity, and Ava's 89% fertile window detection trails Tempdrop's 99%. It's also not recommended for women with very irregular cycles (a significant portion of TTC women with PMOS).
Femometer Ring
The budget option. At $99, the Femometer Ring is the most affordable wearable on this list. The ring form factor is discreet and comfortable for most users. But it lacks peer-reviewed accuracy data, and the app is basic compared to Tempdrop and Ava. Good as a starter device, but if accuracy matters to you (and it should), Tempdrop is worth the extra $90.
Do You Even Need a Wearable?
No. You can track BBT with a $12 oral BBT thermometer and get the same data — you just have to take your temperature at the same time every morning before getting out of bed. If that routine works for you, a wearable is a convenience, not a necessity.
Wearables become worth it if you have inconsistent wake times, if you're a shift worker, if you have a baby that wakes you at random hours, or if you've tried oral BBT and found the routine unsustainable.