Reading, the honest objection
Home dopplers, what midwives actually warn about
The NHS tells you plainly not to use a home doppler to check your baby's heartbeat yourself. That advice is right, and the reason behind it applies to microphone apps too, ours included. So here is the whole argument, including the part that does not flatter us.
The third clip is real audio with no rhythm in it. Watch what an honest verdict looks like.
Firstsong is not a medical device, it is not a doppler and it does not use ultrasound. It cannot tell you that your baby is well and neither can a doppler. If you have noticed fewer movements than usual, or a change in the pattern you know, call your midwife or maternity unit now. Do not listen to anything first.
What is actually happening: emitting against listening
A doppler is an active device. It transmits ultrasound into your abdomen and measures the frequency shift of what comes back off moving tissue, which is why it can pull a rhythm out of a body that a passive device gets nothing from. It is not searching for a faint sound. It is making its own signal and reading the echo.
A microphone app is the opposite. It emits nothing at all. It records the sound already leaving your abdomen, filters out everything above the band where heart sounds live, and amplifies what is left. That is the same physics as a stethoscope, with better arithmetic behind it.
This is a real difference and it is worth being precise about, because it cuts both ways. Nothing goes into your body from a microphone. It also means a microphone loses every fight a doppler wins: through a thick abdominal wall, through an anterior placenta, on a bad day, the doppler will often find a rhythm where the phone finds silence. This is not a substitute for a doppler and we are not going to sell it as one.
Why midwives warn about them, and it is not the ultrasound
Read the NHS page on your baby's movements and the warning is unambiguous. Do not use a home doppler to try to check your baby's heartbeat yourself, because it is not a reliable way to check your baby's health, and because even if you hear a heartbeat that does not mean your baby is well. The full page is here.
Notice what that warning is about. It is not a claim that ultrasound at these levels harms anyone. It is a claim about what happens next in the kitchen at midnight, and the sequence is always the same.
- Something feels different. Fewer movements than usual, or a pattern that has changed.
- The device comes out, because it is right there and a phone call feels dramatic.
- A rhythm appears. It might be your baby, it might be your own pulse doubled, it might be flow through the placenta keeping time with you.
- The fear drops. The call does not happen tonight.
- The harm, when there is harm, is in the hours between step four and the call that eventually gets made.
That is the whole objection, and it is a good one. It has nothing to do with the technology and everything to do with what a reassuring noise does to a frightened person's judgment. The UK charity Kicks Count campaigns on exactly this point.
Where a microphone app sits in that argument
Honestly, on the same side of it. An app that hands you a confident number after reduced movements can cause the same delay as a doppler, and the fact that it emitted nothing into your body is no comfort at all if it talked you out of the call.
| Home doppler | Microphone app | |
|---|---|---|
| Sends energy into your body | Yes, ultrasound | No, it only listens |
| Finds a rhythm through a difficult belly | Often | Frequently not, which is the trade |
| Can report your own pulse as a baby | Yes | Yes, unless it is built not to |
| Can tell you your baby is well | No | No |
| Can delay a call you should have made | Yes | Yes |
What actually helps
- Learn your own baby's pattern. The NHS is explicit that there is no set number of movements to expect and no need to count kicks. What matters is what is usual for your baby, so that you can notice when it changes.
- Never use any device to decide whether to call. That is the rule that makes the rest of this safe. Decide first, listen afterwards if you still want to.
- If you already own a doppler, change what it is for. Using it because hearing your baby is lovely is a different act from using it because you are frightened. The second one is the one midwives are warning about.
- Check any number against your own pulse. Count for thirty seconds, double it, divide. The full check takes half a minute.
- Treat silence as nothing at all. Not finding a rhythm is not evidence of a problem any more than finding one is evidence of safety. Why that is.
When to call your midwife
Now, if anything about the movements has changed. The NHS says to call immediately even in the middle of the night, and maternity units mean it. Nobody minds the call that turns out to be nothing, and the people who take these calls would far rather have ten of those than one that came the next morning.
There is no number of movements you are supposed to count to, and there is no device on this page or any other that can replace the sentence this is not what my baby normally does.
How Firstsong handles this
The behavioural risk is the one we designed against, because it is the only one we can do anything about. Firstsong can end a session with nothing, and does. It reads your real pulse from your Apple Watch or your camera and refuses rhythms that match it, so a doubled maternal heartbeat does not get handed to you as a baby. It repeats the movements advice after every session, including the ones that worked, because that is the moment it matters. And it never sends you a notification suggesting it is time to check on your baby, because manufacturing that impulse is how this whole problem starts.
The engine, running on three public recordings in this tab. One is a mother, one is nothing at all.
One email, the day it opens
Firstsong is not on the App Store yet. Leave an address and you get exactly one message when it is, with the price on the first line. No newsletter, no drip, no partner offers. You can reply to that email and a person reads it.
Stored on our own server, never sold, never shared. Your IP is hashed, not kept. Nothing about your pregnancy is asked for or stored.
The bottom line
The midwives are right, and the reason they are right is not the ultrasound. It is that a comforting sound arrives exactly when your judgment is worst, and a heart rate at one instant cannot say anything about how a baby is doing across an evening.
A microphone app puts nothing into your body, which is a genuine difference and a small one. The difference that actually matters is whether the thing in your hand is willing to tell you when it has found your own heart, when it has found nothing, and that neither answer is a reason to skip the call.
Common questions
Is ultrasound from a home doppler dangerous?
That is not the argument the NHS makes and it is not the argument we are making either. The stated reason is that a home doppler is not a reliable way to check your baby's health and that hearing a heartbeat does not mean your baby is well. The risk being described is a delayed call, not a damaged baby.
So is your app safer than a doppler?
It emits nothing, which is a real technical difference. It is not a safer way to reassure yourself, because reassuring yourself with any device is the behaviour being warned about. Where an app can genuinely do better is in refusing to produce a number it cannot stand behind.
Should I throw my doppler away?
That is between you and your midwife, and it is worth actually asking them. What is worth changing today is when you reach for it. Never after reduced movements, and never to decide whether to make a call.
Why build a listening app at all, then?
Because wanting to hear your baby is not a medical impulse and does not need to be treated as one. The problem was never that women listen. It was that the tools lie to them, and that is a fixable engineering problem.
Will you ever claim this replaces a doppler?
No. A doppler will find a rhythm in situations where a passive microphone finds silence, and pretending otherwise would be the same dishonesty we built this whole thing to avoid.
Keep reading
- What the silence actually means. why finding nothing is not evidence of anything
- Is that my heartbeat or the baby's. the doubling trap, and the check that catches it in thirty seconds
- The arm test. how to find out whether an app measures anything at all
- Hear the difference. an engine deciding, and refusing, on three real recordings
Last checked 2026-08-23