Manufacturer: TempDrop LLC, Israel

*Price: Basic - $159, Confidence - $199 (Basic + 1-year full refund window), Freedom - $249 (Confidence + TempDrop Care insurance cover + extra battery and armband)

How does it work? Basal body temperature (BBT) device worn overnight that collects continued temps as you sleep. A small sensor is held in the armpit with an elastic band. Data is downloaded daily to an app (user decides when) which uses an algorithm to define your lowest BBT of the night. App reports a single value to use in any NFP method that integrates BBT as a daily observation.

Science behind it: Discussion with the manufacturer indicates they have a well-thought-out algorithm to pick the “correct” BBT among the 20,000 readings captured every night. App contains a “temperature smoothing function” that retroactively adjusts previous temps after about 14 days of data are collected which the manufacturer believes better filters to find the best temperature to report. This makes the temp curves look nice, but it is unknown if this helps or hinders effectiveness of using the adjusted temps in an NFP method. Until we know more based on scientific studies, we recommend ignoring the adjusted temps and relying on the daily value provided entered in a separate tool (app or paper chart). Users often comment the armband ($29) has a small replaceable plastic armband frame that breaks.  The manufacturer will replace the frame component of the armband at no cost under their warranty policy. A new, stronger frame has been developed to address this issue.  Two other apps currently automatically synch with TempDrop: Chart Neo (Apple) and Ovuview (Android).

Who might this help? Those who feel oral morning BBT is unreliable due to interrupted sleep patterns. Many users report they like this way of collecting BBT and feel it is as good as oral morning temps with more convenience.

Who doesn’t this help? Those who have trouble remembering to take their temp. Women who frequently forget oral morning BBT might just as likely forget to put the device on before bed. Also, uninterpretable temp patterns that not due to irregular taking times or missed sleep are unlikely to be better with TempDrop versus a $10 oral BBT. Lastly, Temp Drop does not help those using it alone to TTA as it does not identify the fertile window--it should be used as part of a scientifically based Sympto-Thermal FABM.

Manufacturer: Cambridge Temp Concepts, Cambridge UK

*Price: $85/month

How does it work? Intended for those seeking pregnancy, this temperature recording device is intended to identify the day of ovulation up to 10 days in advance. Sensor held in place by an armband and worn overnight. Each day it syncs with a companion app that makes a determination of ovulation day by an undisclosed temperature algorithm.

Subscribers also have access to “fertility coaches” who will check in after the first and second month of data is collected to provide a review of the cycle in order to help achieve pregnancy.

Science behind it: While a very small study of eight women showed good correlation to ultrasound-detected ovulation (Rollason et al (2014)), there is no published data yet on actual pregnancy rates from a large group of women using the device. Importantly, there is no data available if this is better than other low or no-cost means to identify days with the highest probability of pregnancy.

Who might this help? Women who have been TTC without success over a few months. However, this is an expensive way to define the most fertile days. For less than the cost of two months' use of Duo Fertility, women can take a FABM course and learn about all of the signs of fertility that can help pinpoint their fertile time (and know how to chart for a lifetime).

Who doesn’t this help? Those who have trouble remembering to take their temp. Women who frequently forget oral morning BBT might just as likely forget to put the device on before bed. Also, uninterpretable temp patterns that not due to irregular taking times or missed sleep are unlikely to be better with Due Fertility versus a $10 oral BBT. Lastly, Duo Fertility does not help those using it alone to TTA as it does not identify the fertile window.

Manufacturer: Raiing Medical Group, Beijing China

*Price: $129

How does it work? This is a temperature device worn overnight that collects continuous temps as you sleep. A small sensor is held in the armpit with an adhesive patch. Data is downloaded daily (user decides when) to an app which uses an algorithm to define the lowest BBT of the night. App reports a single value to use in any FABM that integrates BBT as a daily observation.

Science behind it: The manufacture first developed core temperature recording devices for use in surgical procedures and this is an extension of that technology. There is no published data on its use in any FABM. A small, unpublished test comparing oral BBT to iFertracker BBT among 17 experienced STM users revealed poor correlation of iFertracker temps with oral temps, and in 40 percent of cycles the end of the fertile window was delayed when iFertracker temps were used instead of oral temps. On a scale of 1 to 10 with 10 being the best, the testers rated iFertracker an average of 4.0, and their likelihood of recommending to a friend at 3.8. Complaints about irritation from the adhesive were far more common than expected, and battery life was surprisingly short (iFertracker now comes standard with a replacement battery).

Who might this help? Women who are convinced overnight BBT recording is a must-have but can’t find the extra $30 to buy TempDrop Basic.

Who might this not help? Those who have trouble remembering to take their temp. Women who frequently forget oral morning BBT might just as likely forget to put the device on before bed. Also, uninterpretable temp patterns that not due to irregular taking times or missed sleep are unlikely to be better with iFertracker versus a $10 oral BBT. Lastly, iFertracker does not help those using it alone to TTA as it does not identify the fertile window.

Manufacturer: AvaCo, Zurich, Switzerland

*Price: Ava Basic - $259 (bracelet + app); Plus - $299 (basic + refund if not pregnant in 12 months + ebook on fertility); Premium - $359 (Plus + refund in 6 months if not pregnant)

How does it work? A device that is worn overnight on the wrist, Ava records fie signs: skin temp, resting pulse, heart rate variability, perfusion (the rate at which blood is delivered to tissues), and breathing rate. The manufacturer states this is FDA recognized as a Class I medical device (like dental floss and bandages) and “detects an average of 5.3 fertile days with 89 percent accuracy.”

Science behind it: There is only one published study that correlated wrist skin temperature changes with the LH surge (a signal of ovulation in the next 24 hours). However, only cycles that had 80 percent of cycle day temps captured were used in the evaluation, and many experienced NFP users only capture temps on about 70 percent of cycle days. There are other not-yet-published studies showing that the heart rate changes slightly from the beginning to end of the cycle, but there is no data showing that recording this will allow women to identify the days nearest to ovulation in real time. No data is available on actual pregnancy rates when using Ava compared to nothing, or compared to an alternative method to identify fertility.

Who might this help? It is uncertain whether this may help in TTC. Wearing a device on your wrist while sleeping is convenient, but the data collected needs to demonstrate it can predict the fertile days in real time and at significantly better than other low or no-cost alternatives to justify the high price.

Who doesn’t this help? Will not help those TTA because it does not identify the fertile window.