The headline is somewhat misleading.
The device tracks progesterone levels via saliva. It's currently possible to track those levels via urine or blood, but saliva is probably the most convenient.
But here's the catch. If you desire to avoid pregnancy, you avoid sexual activity during the fertile window that the device indicates. This is known as a fertility awareness method, and in Catholic circles it's also known as natural family planning.
It is not a contraceptive in the sense that it allows you to have sex during the fertile part of your cycle but not get pregnant.