When Apple released its iOS9 mobile operating system it included a new feature - the ability for women to log their sexual activity alongside details of their menstrual cycles.
An earlier version of its HealthKit software - which tracks everything from electrodermal activity to chromium intake - had lacked the facility.
Other apps existed that could pick up the slack, but it had led to claims that Apple - and other phone companies - had not focused closely enough on women's health.
Samsung's S Health and Android's Google Fit have yet to add this feature into their health apps, but it's likely to only be a matter of time before they do.
Women who are trying to get pregnant often track a number of health signals in order to fully understand their monthly cycle and therefore catch their most fertile times - much as a marathon runner would track their fitness metrics.
According to Apple, users decide which information will go into the Health app and which third-party apps can access the data.
Those third-party apps must have a privacy policy.
When phones are locked, the health and fitness data is encrypted. If users choose to back up health data to iCloud, that is encrypted as well.
"A lot of people are monitoring data that helps them plan for a family," says Ricky Bloomfield, a doctor at Duke University who is currently engaged in trials for HealthKit with his patients.
"The impact here can be quite significant in giving users tools to do that more accurately."
The categories people can track include sexual activity, including whether protection was used, basal body temperature, cervical mucus quality, menstruation, ovulation test results and spotting.
Dr Nathaniel DeNicola, a gynaecologist at the University of Pennsylvania, said the sex-tracking technologies had the power to help people take more charge of their health care and communicate better with their doctors.
Gynaecologists take the last menstrual period as a vital sign and when women can log it in their phones, they are much more likely to have accurate dates on hand, said Mr DeNicola.
"It's almost ubiquitous now that women will have an app to track their pregnancy," he said.
He does not always recommend patients track their reproductive health via an app, but he asks patients about it and tells them it can be useful.
There are no studies proving that these apps improve the chance of getting pregnant, or cure diseases, but this kind of digital recording can enhance patient memory, he said.
Often, questions asked at the gynaecologist's office can turn into a "guessing game".
Patients used to do a diligent job with pen and paper, tracking activity when trying to get pregnant. Now it has gone digital.
"It's pretty clear if they're putting it in the phone, it'll increase recall, and help us in dating pregnancies," he said.
Mr DeNicola notes that apps to track health are "inherently fraught with limitations".
"I think we always see tech as having risks...but since the evolution seems inevitable, we may as well find the positive," he said.
Tara Culp-Ressler, a Washington, DC-based journalist who tracks reproductive health issues closely, said the tech giant's announcement was a welcome change to views on women's health in 2015.
"Regardless of whether women think it's a useless app compared to other tracking apps - it is a good step to see such a huge company, especially one that's been criticised in the past, really stepping up and making a statement that women's health and hygiene is integral part of healthcare," says Ms Culp-Ressler.
Reproductive organs are just another part of the body one might want to track like heartbeat or sleep patterns and that message coming from Apple is an important one, Ms Culp-Ressler said.
Megan King, who lives in New York City, had used Clue - one of the other reproductive health trackers - for about a year before iOS9 was released.
Such apps are a good way to track menstrual cycle and fertility, she said.
"This is the year of females owning their feminine hygiene," she added.
"Apple integrating is a huge step forward because it's showing its support of women being aware of what's going on in their own body, and they want it to be something important to everyone."
Would you go around telling people when you've had sex?