A new app and device promises to let you hear your developing baby's heartbeat without the use of a doctor's ultrasound device.

It's called Shell, and it was developed by Bellabeat.

The free app, available now on Apple's App store, uses the microphone on your cellphone to listen to the baby's heart.

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It allows parents to listen to the baby's heart, record it and share on social media or email.

There's an add-on device that snaps onto the phone to help amplify the sound.

The device has sold out, according to the Bellabeat website, but the company says the app works without it.

The website Digital Trends says the Shell add-on will be available on the Bellabeat website in mid-December and retails for $70.