Tempdrop is an Israeli company that makes a fertility sensor worn on the upper arm during sleep. The sensor sits in a soft elastic band and is aimed at people charting ovulation, whether to conceive or to avoid it.

How it works

Body temperature falls to its lowest point during sleep and settles slightly higher after ovulation, and that small shift is the whole signal. Two thermometers and a motion sensor record temperature and movement all night, and an algorithm learns the wearer's own pattern so broken sleep and a warm room can be filtered out. In the morning one reading syncs across and lands on a chart alongside other cycle symptoms.

Key considerations

The chart confirms ovulation after it has already happened, so the method needs several cycles before it says much.