How to turn an old phone into a baby monitor

Yes, it works. An iPhone or Android phone you stopped carrying two years ago has a better sensor, a better microphone, and a faster processor than most monitors sold as baby monitors. You do not need to buy a camera to watch a crib tonight.

The catch is not the picture. It is that a phone was designed to be picked up and put down, not to run one job unattended for nine hours in a dark room while plugged in. Everything difficult about this — heat, power, cord placement, whether the app is still running at 3am — follows from that. This guide is mostly about those parts, because they are the parts that decide whether the setup is any good.

Which phones still work

Roughly: an iPhone 6s or newer, and an Android phone from about 2016 onward. But model numbers are a bad way to think about it, because they go stale and because a well-kept older phone beats a thrashed newer one. What actually matters is that four things still work:

• The camera. Any phone camera from the last decade resolves a crib in a dim room better than you would expect. This is rarely the limitation.
• The microphone. Easy to forget to test, and the thing most often damaged by a drop or by water.
• Wi-Fi. It has to hold a connection for hours, not minutes. A phone that drops off the network every so often is fine as a music player and useless here.
• The battery, plugged in. You will run it on mains power the whole time, so capacity barely matters — but the battery still has to be healthy enough to sit at full charge safely.

You will also need the phone to run a current enough OS to install the app you choose. This is usually what rules out the very oldest candidates, not the hardware.

What actually rules a phone out

A swollen or failing battery. If the back of the phone bulges, the screen sits proud of the frame, or it gets alarmingly hot on a normal charge, that phone is finished. Do not put it near a crib — recycle it. This is the one hard no in this guide.

A dead or flaky Wi-Fi radio. Test it by leaving the phone connected and idle for an evening before you rely on it.

An OS too old for the app store. Frustrating, but not worth working around with sideloaded software of unknown provenance on a device pointed at your child.

Do you need an app for this?

The obvious trick is to leave a video call running — FaceTime, WhatsApp, Messenger — between the old phone and yours. It works, for about ten minutes, and then you notice the problems.

A call has no idea what it is looking at, so it cannot tell you anything happened; you have to be watching. Calls drop, and when one does, nothing tells you. Both screens stay lit, which is most of the heat and all of the wasted power. And a call ties up the phone in your pocket, which is the phone you wanted to be doing something else with.

What a purpose-built app adds is the three things a call cannot: it alerts you instead of requiring you to watch, it keeps running with the screen off, and it tells you when it has stopped. If you already have a monitor app you trust, keep it — the rest of this guide applies either way.

Where to put it

Aim for a view of the whole sleeping surface, from far enough back that the baby stays in frame after rolling. A little over a metre away and slightly above the mattress line is usually right. Closer gives you a beautiful picture of one corner of the sheet and nothing else.

The important constraint is not the angle, though. It is the cable.

The US Consumer Product Safety Commission has a specific recommendation here, and it is worth following exactly: place cords at least three feet away from any part of the crib, bassinet, play yard, or other sleep environment, and never position a monitor inside or on the edge of a crib. That alert exists because children have died in monitor cords — CPSC recorded seven strangulations and three near-strangulations between 2002 and 2012, in children from six to twenty months old.

A phone needs a charging cable, so a phone is a corded monitor and this applies to it. Three feet, from every part of the crib, including a cable run down a wall or across a shelf. And re-check it as your baby gets taller and more mobile: a placement that was comfortably out of reach one month is not automatically out of reach the next.

Heat and power: the part nobody mentions

Almost every article about this stops at "point the camera at the crib". Here is what it leaves out.

A phone running its camera continuously, encoding video, holding a Wi-Fi connection, and charging at the same time gets noticeably warm. Not dangerously, on a healthy phone in open air — but warm, all night, every night. That is simply what the job costs.

Three things follow from it:

• It has to stay plugged in. No phone will do this on battery. Plan the setup around a socket.
• It needs air on every side. Standing on a hard surface with space around it, not lying flat, not in a thick case, and never on or against bedding, a pillow, a folded blanket, or anything else soft. Fabric is insulation.
• Phones throttle when they get hot. If a phone is warm enough to slow itself down, the video will stutter before anything else goes wrong — which makes stuttering video a useful early warning rather than just an annoyance.

We are still testing how warm this gets across different models and whether each one holds up for a full night, and we cannot yet give a number that is true for every phone. We would rather say that than publish a figure we got from one handset on one evening. If your phone is too hot to hold comfortably, stop and rethink the placement.

Putting it together

Perhaps twenty minutes, most of it spent on the old phone.

1. Clear the old phone out. If you are done with whatever is on it, factory reset it. If not, at least sign out of accounts you do not want reachable from a device that now lives in another room.
2. Silence everything. This is the step people regret skipping. Cancel every alarm, turn off notification sounds, mute ringtones, and switch off automatic updates that might restart it. A forgotten 6:30am alarm on a phone eighteen inches from a sleeping baby is a bad morning.
3. Get it on your Wi-Fi and leave it there. Connect it, then let it sit idle for an hour and confirm it is still connected. Turn off any battery saver that disconnects Wi-Fi when the screen is off.
4. Install the app on both phones and pair them. The old phone is the one by the crib; yours is the one that watches.
5. Stop the system from killing the app. On Android, exclude it from battery optimisation — otherwise the OS will eventually close it to save power, usually on the night you needed it. On iPhone, keep the app in the foreground on the bedside phone and set auto-lock so the screen turns off without suspending it.
6. Position it, then plug it in. Frame the whole mattress, give it air on every side, and run the cable so it stays three feet from the crib.

Five checks before you rely on it overnight

Run these once, in daylight, before the first night you actually depend on the setup. It takes about two minutes.

1. Framing after a roll. Put something the size of your baby at each corner of the mattress and confirm all four are in frame. Babies do not stay where you put them.
2. Sound, at real volume. Play a recording of crying from the crib at the volume a real cry would have, and confirm the app reacts. Testing with a shout from a metre away proves nothing.
3. Power, end to end. Cable seated, charger in a socket that is not on a switch someone turns off at night, phone actually gaining charge rather than slowly losing it.
4. The alert path, not just the app. Trigger a real alert and confirm it reaches you where you will be — through a closed door, with your own phone face down, on silent or Do Not Disturb if that is how you sleep. This is the check people skip and it is the one that matters most.
5. Airflow and cords. Air on every side of the phone, and every cable at least three feet from the crib.

Then re-run checks one and five every few weeks. Both drift as the baby grows.

What a phone can't do

Being straight about this is more useful than another feature list.

It cannot monitor breathing or heart rate. A camera and a microphone see movement and hear sound. Anything sold as measuring an infant's vital signs from across a room is making a much larger claim than the hardware supports, and we will not make it.

It cannot replace an adult. It tells you something changed. It does not tell you what to do, and it does not know when it is wrong.

It will sometimes be wrong in both directions. It will alert on a car alarm outside and stay quiet through a grizzle you would have got up for. Any system that promises otherwise is either lying or has been tuned to alert on everything.

It stops if the phone stops. An OS that decides to close a background app, a cable knocked out, a phone that overheated and shut down — in every case the monitoring simply ends. A monitor that can fail silently is worse than no monitor, so whatever app you pick, find out how it tells you it has stopped.

Setting it up with Bebrise

Bebrise is our take on this: the old phone by the crib does the watching and listening on the device itself, and the video only ever travels across your own Wi-Fi — it does not reach us, because it does not leave your home. The trade is that you cannot watch from outside the house. How that works is set out on the homepage, along with the things it can't do yet — one caregiver phone at a time is the big one.

It is in small-scale home testing and is not in the app stores yet. Ask us for the install details if you want to try it. If you would rather use something else, the five checks above still apply.