Test review: iButton – a different basal body thermometer

iButton Review

iButton Test Review

I tried the iButton for one cycle. This is my personal opinion about this special basal body thermometer and I will help you to decide if you should buy it.

Initial remarks:
I have a small son right now myself and I think taking my temperature every morning is quite a challenge. That is why I really wanted to try if the iButton could help me with that. This measuring device is also interesting for women working in shifts. Upon request, I was given the iButton Set for free by the producer Endotherm so I could test the iButton and tell you about it. Thanks a lot for that!  I have been analyzing my cycles since November 2009 with the Symptothermal Method and I compared the cycle curve measured with the iButton with a cycle curve measured with a different thermometer.

How does the iButton work?

The iButton works totally different than normal basal body thermometers. With the iButton you don’t take the body temperature in the morning after getting up, but it is taken during the night in the vagina. To do this, you insert the small iButton-Chip in a silicone case provided to that end and introduce the whole thing in your vagina before going to bed. The chip can stay in the vagina for several days, but it is recommended to boil the silicon case clean every five days. You can connect the chip with an USB adapter to your computer daily as needed to analyze the data. You can use the software that goes with it to programme the chip to for example take the temperature every 30 minutes between 10 pm and 7 am. When analyzing the data, you can always use the temperature at 2 am or at any other time to evaluate your cycle. OR you always take the lowest value of the night, which is how I did it. That is what I would recommend mothers with toddlers, because the night rest might be disturbed at different times. You can either copy the measured temperature values by hand into a cycle sheet or a fertility calendar (another software by Endotherm). This software also works without the iButton, but in this case you have to buy a license after one month to keep on using it.

Handling of iButton & Software

I managed the handling very well and found it very relaxing not to have to take the temperature with a toddler (at least that is what I can very well imagine, because I did take my temperature in the morning anyway to be able to compare the temperature values). I decided to put the iButton in every night and take it out again in the morning. That way though, I had to get used to having to think of inserting the iButton in the evening. I did forget that a couple of times, but that doesn’t affect the cycle evaluation too much. What I found a lot more strenuous was the installation and operation of the software. As I usually only use Ubuntu as an operating system, I was quite disappointed because the fertility calendar only runs on Windows systems. There are currently no (good) solutions for Linux and Mac systems. I think that is a shame. In the end I installed the EndoTherm Control and Basal software on the laptop of a friend. Unfortunately, I didn’t manage to look at my cycle curve with the Basal software. I am sure it works somehow, but unfortunately I didn’t have the time anymore to have a better look at this software, because on the one hand I got frustrated and on the other hand I couldn’t spend hours experimenting with my friend’s laptop. So, in the end I just used the Control software to enter my lowest temperature values from every night into my cycle chart and to compare them with my temperature when waking up in the morning.

Cycle evaluation with the EndoTherm Basal iButton compared to the cyclotest 2 plus Thermometer

I programmed the iButton-Chip so that it would record a measurement every 10 minutes. Parallelly to the iButton measurement I took my temperature with the cyclotest 2 plus in the morning and put down these values in my cycle chart. When comparing the cycle curves, you can clearly see that the iButton curve (red curve) is lower than the curve of the temperatures taken in the mornings. I was able to evaluate the iButton curve perfectly as well and it showed the same fertile days and the same first higher measurement. I should mention as well that the measuring accuracy of the iButton is 0.1°C and the measuring resolution is 0.0625°C. In theory the studies about the Symptothermal Method showed that a resolution of 0.05°C is necessary. This is explained in further detail in the iButton FAQ. I myself couldn’t make out any negative impacts on my cycle curve though. On the contrary, the iButton curve allows for a much clearer evaluation and shows a nice and steady curve. It could be coincidence though as well, because I have only tested it for one cycle until now. It would have been interesting now if I had an interruption if it would have had an influence on the body temperature at night, or less or even not at all? Unfortunately, when I had an interruption on the 9th cycle day, I didn’t measure at the same time with the iButton in the test cycle. I will continue measuring and tell you when I got it in black and white. In the following pictures you can see how the curve looks in the software, with the evaluation I added (dots, lines etc.). Furthermore, I put down the temperature curve I measured with the iButton in the cycle chart and compared it to the temperature curve I measured with the cyclotest 2 plus.

iButton - Measurement Software Body Basaltemperature

I marked here the lowest temperature values during the low-temperature phase (blue dots) and during the high-temperature phase (red dots), as well as the auxiliary line through the highest of the 6


iButton Test Review - Comparison with cyclotest

Evaluation of the temperature curve measured with the iButton (red curve) compared to the blue curve measured with cyclotest 2 plus. Both curves can be evaluated, but to keep a clear structure I only put in one evaluation.

Evaluation of the temperature curve measured with the iButton (red curve) compared to the blue curve measured with cyclotest 2 plus. Both curves can be evaluated, but to keep a clear structure I only put in one evaluation.


You can find a contact form and a telephone number on the homepage of the producer, so you will surely get help there if you have any questions.

Conclusion & help with purchasing decision for the iButton Set

All in all, I think that the measurement with iButton has some advantages but also some disadvantages. It can be quite helpful to measure with the *iButton if you have small children, work in shifts, often get up at very different times or have other problems that keep you from taking your basal body temperature for three minutes in the morning. You have to be aware though, that it is a bit more complicated to read the temperature value than with a normal thermometer, especially if you don’t have a Windows PC. Until now there are no studies concerning the iButton, but there are many positive experiences and reports you can find in the Fertility Awareness forum. Financial disadvantage: The iButton-Set obviously is a bit more expensive than a normal basal body thermometer. Eventually every woman has to decide for herself what is more important to her and if the iButton can offer THE solution for her current situation. I hope I was able to help with your decision-making process.
Fertile greetings!

Yours, Anne


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