# Firstsong > Firstsong is an unreleased iPhone app for the third trimester of pregnancy. It amplifies and filters the real sound of the mother's abdomen so she can hear it through headphones, prints a fetal heart rate only when the evidence holds for at least 30 seconds, and tells her when the rhythm it found is her own heart rather than the baby's. - The engine is fetal phonocardiography, not doppler and not ultrasound. It is a passive microphone. Nothing is emitted into the body. - It runs entirely on the device. No audio, no heart rate and no gestational age ever leaves the phone. - The signal engine was validated on public PhysioNet databases before any interface was designed. On 116 third trimester abdominal recordings it detected a stable in band rhythm in 97 of them, 83.6 per cent, and against the CTG reference on the 103 recordings that carry one the mean absolute error was 2.69 beats per minute. - On 372 adult heart sound recordings with a true rate below 110 beats per minute, used as a negative set, exactly one was classified as fetal. - The same engine is ported to JavaScript and runs live on the website, on three public recordings, so the claims above can be checked in a browser without installing anything. - Those numbers come from recordings made with dedicated research sensors, not from an iPhone microphone on a real belly. That measurement does not exist yet and the site says so. - The team has no clinicians on it. Nothing on this site is reviewed by a doctor and no page claims otherwise. ## What this app does not claim - It is not a medical device, not a doppler and it does not use ultrasound. - It cannot diagnose anything, cannot rule anything out and cannot tell you that a baby is well. - It makes no promise before week 28 of pregnancy. Below that week the public evidence the engine was validated on is four recordings, which is not enough to promise anything. - Silence is a real answer. When nothing holds, it says nothing was found instead of showing a number. ## Pricing - Annual: 79.99 USD per year, about 1.54 per week - Weekly: 12.99 USD per week, about 675 per year if you keep paying weekly - There is no free trial and no introductory price. The first listen inside the app is real and complete, and you decide after it. That is the trial. ## Pages - [Home](https://digitalnafta.com/firstsong/): What the app does, what it refuses to do, and what it costs. - [Hear the difference](https://digitalnafta.com/firstsong/hear-the-difference): Three real recordings from a public research database, analysed live in this page by the same engine Firstsong ships with. ### Answers - [Anterior placenta and hearing a heartbeat at home](https://digitalnafta.com/firstsong/anterior-placenta-heartbeat): A placenta at the front sits between the microphone and the baby and soaks up the sound. What that changes, what actually helps, and what it does not mean. - [Are baby heartbeat apps safe](https://digitalnafta.com/firstsong/are-baby-heartbeat-apps-safe): A microphone app puts nothing into your body, unlike a doppler. The physical answer is the easy half. The risk worth talking about is false reassurance. - [What a baby heartbeat app actually is](https://digitalnafta.com/firstsong/baby-heartbeat-app): A baby heartbeat app is a microphone and a filter, not a doppler. How the category really works, why most of them disappoint, and what we measured first. - [A recording is only worth keeping if the heart in it is the right one](https://digitalnafta.com/firstsong/baby-heartbeat-recorder): Recordings that stay on your iPhone and in your own iCloud, saved next to the verdict that produced them, shared as a plain audio file, with no account anywhere. - [How to judge one of these apps without trusting anybody](https://digitalnafta.com/firstsong/best-app-to-hear-baby-heartbeat): No winner at the top of this page. Eight checks you can run on any app in this category in five minutes, what the reviews measure, and what the market charges. - [Do baby heartbeat apps work](https://digitalnafta.com/firstsong/do-baby-heartbeat-apps-work): Sometimes yes and often no. It depends on the week, the placenta, the room and the phone. Here are the measured detection rates, and what the category hides. - [An app is not a doppler, and that is the whole point](https://digitalnafta.com/firstsong/fetal-doppler-app-alternative): A home doppler transmits ultrasound. A phone only listens. What the NHS says about using one at home, and what an app is honestly for instead. - [How to actually listen at home](https://digitalnafta.com/firstsong/hear-baby-heartbeat-at-home): A quiet room, wired headphones and a phone flat on bare skin. Where to place it, how long to wait in each spot, and how to tell your own pulse apart. - [What makes this an iPhone app, and not yet an Android one](https://digitalnafta.com/firstsong/iphone-baby-heartbeat-app): Why iOS first, where the microphone actually sits on your iPhone, and why the call optimized capture path deletes the exact band a small heart lives in. - [Is it my heartbeat or the baby](https://digitalnafta.com/firstsong/is-it-my-heartbeat-or-the-baby): Your pulse is the loudest thing in your belly, and doubled it lands right in the fetal range. Why apps fall for it, and the wrist test that settles it. - [What it actually sounds like when a phone finds it](https://digitalnafta.com/firstsong/listen-to-baby-heartbeat): A muffled double knock under 200 Hz, not the clean gallop of a doppler. What a phone can pick up through a belly, why headphones are required and why a cable wins. - [When you can hear a baby heartbeat at home](https://digitalnafta.com/firstsong/when-can-you-hear-baby-heartbeat): A phone is a third trimester instrument. What the public data shows from week 28 on, why nothing is promised earlier, and the strangest chart in this category. ### Reading - [Anterior placenta, and why your belly sounds further away than everyone else's](https://digitalnafta.com/firstsong/reading/anterior-placenta-why-it-sounds-further-away): The front wall is an ordinary place for a placenta to sit. It is also directly between your baby and the microphone. What that does to sound, and what to do. - [Home dopplers, what midwives actually warn about](https://digitalnafta.com/firstsong/reading/home-dopplers-what-midwives-warn-about): The warning is not really about the ultrasound. It is about what a reassuring sound does to the phone call you were about to make. And what an app is not. - [Is that my heartbeat, or the baby's](https://digitalnafta.com/firstsong/reading/is-that-my-heartbeat-or-the-baby): A resting pulse doubled is the failure mode of this whole category. The physics of it, a check you can run with your own hand, and what an honest engine does. - [The arm test, and what it tells you in thirty seconds](https://digitalnafta.com/firstsong/reading/the-arm-test): Put the phone on your forearm, then on a cushion. An honest app gives an adult rate on one and nothing on the other. Run it on every app in this category. - [What a phone can and cannot pick up, week by week](https://digitalnafta.com/firstsong/reading/week-by-week-what-a-phone-hears): Detection rates we measured band by band across the third trimester, why the middle dip is not real, and the honest reason nothing is promised any earlier. - [You cannot hear anything, and it is the middle of the night](https://digitalnafta.com/firstsong/reading/what-silence-actually-means): A phone that finds nothing has told you about the room, the angle and the week. It has not told you about your baby. What blocks the sound, and what does matter. ## Contact - Support and press: reply to any email from the list, or use the support page.