There’s a new form of birth control for the digital age, and it seems almost too good to be true. Maybe you’ve seen ads for it: a form of birth control that is non-hormonal, extremely effective, and comes with no unpleasant side effects — birth control apps.

With names like Natural Cycles and Daysy, they promise to help people with periods track their ovulation so they know when they’re fertile. By avoiding unprotected, penetrative sex during the fertile window, the apps claim, you can prevent pregnancy without the frustrations or risks of hormonal birth control or copper IUDs.

With all the potentially unpleasant side effects that can come along with other methods of birth control, the idea of an effective, side-effect free option is certainly compelling. Moreover, the apps boast impressive-sounding scientific backing for their efficacy claims: one of the apps, Natural Cycles, was developed by a Swedish scientist who helped discover the Higgs Boson, and was just given approval by the FDA last year.

Both Natural Cycles and Daysy have peer reviewed studies in prominent journals affirming their efficacy. But these apps are also dogged by controversy: the UK banned ads from Natural Cycles that claimed the app was “clinically tested” and “highly accurate” and the Swedish conducted an investigation into Natural Cycles after a women’s clinic reported that 37 of its patients had sought abortions after becoming pregnant while using the app. A journal article by Dr. Chelsea Polis published last year argues that the research backing up Daysy is fundamentally flawed.

So what should you know before you rely on an app for your birth control?

The apps may not suit your lifestyle or daily habits

Natural Cycles and Daysy work by measuring your temperature with a basal body thermometer, which measures tiny fluctuations in body temperature that can signal ovulation. However, in order to get an accurate temperature reading, users need to have a fairly regular sleeping pattern and need to take their temperature immediately upon waking up. If those stipulations don’t suit your lifestyle, the app may not be the best choice for you.

Not all menstrual cycles are created equal.

Natural Cycles and Daysy work by tracking your basal body temperature over a period of months, and using the data to predict when you’ll ovulate. However, the algorithms rely on the assumption that your cycle is regular and predictable. If your menstrual cycle tends to be irregular, it could impact the app’s ability to predict your fertile window. (For their part, Natural Cycles says that if the app sees something unusual or unexpected, it will tell users to avoid intercourse on that day by default.) Given that the app relies on your cycles being predictable, you won’t be able to transition straight off of a hormonal method of birth control, like the pill, and on to a birth control app, since your cycle will take a while to become regular again.

They can be expensive

Daysy will set users back $330, according to the company’s website, while Natural Cycles costs $79.99 for a year-long subscription and a thermometer.

The apps won’t protect against STIs.

Because the apps only give you information about when you’re fertile, they do not provide any protection against STIs. You’ll need to use another contraceptive method for STI prevention, if that’s a concern for you.

The research is disputed

Dr. Chelsea Polis, a researcher from the Guttmacher Institute, published a journal article in “Reproductive Health” last year arguing that the research backing up Daysy’s claims of effectiveness was flawed, and could place users at a heightened risk for unplanned pregnancy. In a blog post on her personal website, she says that the research supporting Daysy’s effectiveness relied on methods that were “flawed and inconsistent with accurate approaches to estimating effectiveness – making their results void of meaning.” For their part, Daysy issued a statement acknowledging that their app “is not a contraceptive in the real sense.”

Both partners need to be responsible for pregnancy-prevention

Ultimately, although birth control tends to fall on the people who can become pregnant, both partners in a relationship need to be responsible for making reproductive decisions and preventing pregnancy. If hormonal birth control or app-based birth control aren’t right for you and your partner, there are a number of other options that are available. You should have a conversation with your partner and a doctor to determine what method will work best for the both of you. Whether you use an app, an IUD, a pill, a barrier, or any other method of birth control, preventing pregnancy should be a joint effort.