12/10/2014 09:06 am ET Updated Dec 10, 2014

Return Of The Rhythm Method

ANNA HYMAS via Getty Images

Tired of condoms and the Pill, many women are turning to new apps that help them practice one of the oldest forms of contraception.

Every morning when she wakes up, Becca, a college student in Pennsylvania, puts a teardrop-shaped thermometer called the Daysy under her tongue. If it lights up green, she knows that day she and her boyfriend can have sex without a condom. If it’s red or yellow, they need to use protection.

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