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(Pocket-lint) - Bellabeat, the company that makes health trackers designed to look like jewelry, has developed an app for expecting parents.

The new app, called Shell, works with an add-on. Together, they can record and listen to fetal heartbeats - without any Doppler technology. The Shell wraps around your iPhone much like a phone case and works with the free Shell app, which launched 1 November, to make it easy for you to capture a baby's heartbeat and share it. The Shell app records the sound of your womb via the iPhone's built-in microphone.

While the new app can isolate the sound of the heartbeat through an algorithm that "amplifies key tones and filters out background noise", the Shell add-on has a horn that focuses the sound waves of a fetal heartbeat and improves the sound reproduction of your iPhone's speaker. It also physically separates the mic and speaker, cancelling all possible sound oscillations.

Shell is basically a non-invasive prenatal monitor that amplifies the sound of your baby's heartbeat. Belkabeat has experience in making wearables for the fashionably-conscious, so it's describing the add-on as having a shape and functionality that resembles a seashell. The wave pattern "illustrates the soothing rythmic sound of the heartbeat," it explained.

The Shell add-on, which is compatible with iPhone 6 and newer models, sells for $70 and will be available on the Bellabeat website in mid-December, but you can already start playing with the free Shell iPhone app. Bellabeat had a million people on the app's waitlist at launch.

There's no word yet if an Android app is in the works.

Writing by Elyse Betters.