A baby room thermometer has one job: checking that the room where your little one sleeps stays between 18 and 20 °C. That is the range recommended by France's national health authority, the Haute Autorité de santé (HAS), and by the French health insurance service, the Assurance Maladie. A simple, easy-to-read, well-placed model is all you need in the vast majority of cases.
How warm a room feels to an adult walking in is a poor guide. You've come from a warmer or cooler room, you're dressed differently, you're moving about. The thermometer replaces that impression with a number. You then use that number to choose your baby's nightwear and the tog rating of their sleeping bag.
Why measure the temperature in your baby's room?
The HAS recommends a moderate room temperature of between 18 and 20 degrees in the child's bedroom. We've set out these guidelines in detail in our article on safe sleep for infants according to the HAS. The Assurance Maladie gives the same range and adds that the room should be aired every day.
The main risk isn't a slight chill but overheating. A baby who is wrapped up too warmly in a room that is too hot can't take off a layer of clothing. The Assurance Maladie also advises against piling on layers and recommends a sleepsuit or a sleeping bag rather than a sheet or a duvet.
So the thermometer has a very practical use: it tells you whether the room is within the target range, above it or below it. It also shows you how the temperature changes between bedtime and the middle of the night, when the heating goes down or a window has been left ajar.
The different types of room thermometer
The simple room thermometer
This is the basic model: a screen or dial that shows the room temperature. It does nothing else, and that is often enough. Analogue versions with a needle work without a battery. Digital versions are easier to read at a glance, provided the screen has good contrast.
The thermo-hygrometer
It shows both the temperature and the humidity level of the air. The recommended humidity in a home is between 40 and 60%. This second figure is useful if the air feels dry in winter or, on the contrary, if condensation appears on the windows. It saves you buying a device you don't need: we explain why in our guide to the baby humidifier.
The thermometer built into another device
Many baby monitors, night lights and alarm clocks display the room temperature. That's handy if the device is already in the room. However, the reading is taken wherever the device sits, often near a plug socket, and is sometimes affected by the device's own heat. If you go for this option, have a look at our criteria for choosing a baby monitor.
The smart thermometer
It sends the temperature and humidity to your phone and keeps a history. That history is genuinely useful in the first few weeks: it shows what time the room cools down or warms up. Once you know how the room behaves, a simple model does the same job. A smart thermometer also needs an app, an account and sometimes updates.
Baby room thermometer: what to look for when choosing one
- Readability. Large, high-contrast numbers you can read from the doorway without switching on the main light. A soft backlight on demand is better than a screen that stays lit all the time.
- A display to a tenth of a degree. This lets you spot a trend, for example a room that drops from 19.5 to 18.2 °C overnight.
- Minimum and maximum readings. A memory for the extremes shows what happened while everyone was asleep.
- A built-in hygrometer. Useful, for a small extra cost, if your home is heavily heated or, on the contrary, damp.
- The power source. Standard battery, button battery, cable or no power at all. This has safety implications, explained further down.
- No unnecessary light or sound. A flashing screen or an hourly beep has no place in a baby's room.
- Sturdiness. A simple casing with no small removable parts that can survive being dropped.
Models with ‘smileys’ that show a happy or sad face depending on the temperature are easy to read, but they hide the number. And it's the number you need to choose what your baby wears. Go for a numerical display, ideally backed up by a colour code.
Where should you place the thermometer in the room?
The rule is simple: measure the air your baby breathes, where they sleep. Place the thermometer at cot height, about one metre off the floor, on a piece of furniture or fixed to the wall.
Some spots give false readings and are best avoided:
- above or next to a radiator, which pushes the reading up;
- on a windowsill, exposed to the cold glass or the afternoon sun;
- against a poorly insulated outside wall, which is colder than the air in the room;
- near an electrical device that gives off heat, such as a night light or a charger.
The thermometer never goes inside the cot or on its bars. It must stay out of your child's reach, including once they start pulling themselves up and grabbing whatever is around them. A device on a chest of drawers next to the cot comes within reach sooner than you might think.
What to do when the temperature is outside the target range
The room is above 20 °C
Turn down the heating in the room if you can, rather than airing it for a long time in the middle of the night. Dress your baby more lightly: a vest and light pyjamas, a sleeping bag with a lower tog rating. Our guide to baby sleeping bags and tog ratings shows which tog rating matches the temperature you've measured. In summer, close the shutters and curtains during the day and air the room when the outside air is cooler.
The room drops below 18 °C
A slight drop isn't a problem if your baby is dressed appropriately. Add a layer under the sleeping bag, or switch to a warmer sleeping bag. Never add a blanket, duvet or pillow to the cot: they are advised against whatever the season. A portable heater should never be placed near the cot.
Check your baby, not just the screen
The thermometer gives you the temperature of the room, not your baby's. To find out whether they are too hot, feel the back of their neck or their back: it should be warm, not sweaty. Slightly cool hands are common and don't mean your baby is cold.
Don't confuse it with other baby thermometers
A room thermometer measures the air. It doesn't replace a medical thermometer or a bath thermometer. A medical thermometer takes body temperature to detect a fever: we compare rectal, forehead and ear models in our guide which thermometer for your baby. A bath thermometer checks the water before your baby goes in; we've looked at whether it is useful or just a gadget.
Some devices claim to do both, for example measuring air and water. One tool per job remains more reliable and easier to look after.
Button batteries: the safety point to check
Many small digital thermometers run on a button battery. The Assurance Maladie specifically lists thermometers among the everyday objects that contain them. If swallowed by a young child, a button battery can cause serious injuries within a few hours.
Before you buy, check how the battery compartment opens. The Assurance Maladie recommends choosing devices whose compartment is closed with a screw or takes two separate actions to open. Keep new and used batteries out of reach. If you suspect your child has swallowed one, call 15 or a poison control centre immediately and do not make your child vomit. Our overview of accidental poisoning in children covers this point in more detail.
A needle thermometer with no battery removes this risk altogether. A model powered by a standard battery in a screw-fastened compartment is also a sensible option.
Do you really need a thermometer in your baby's room?
It isn't an essential purchase, but it is one of the few nursery accessories that delivers a measurable benefit for a few euros. It's especially useful in homes where the temperature varies: badly adjusted communal heating, a loft room, a south-facing room, an older flat. In a house with a very stable temperature, a single thermometer moved from room to room may be enough.
It's useful beyond bedtime too. Awake time is often spent on the floor, where the air is a little cooler. A thick foam play mat insulates your baby from the cold floor during these moments. The thermometer tells you whether the playroom calls for an extra layer.
Sizes, thicknesses and uses are detailed on our baby play mats page.
Key takeaways
- The target is 18 to 20 °C in the bedroom, with the room aired every day.
- A readable model with a numerical display and no disruptive light is enough; a hygrometer is a bonus.
- Place it at cot height, away from the radiator, the window and any devices that give off heat.
- Adjust clothing and the sleeping bag to the reading, never by adding a blanket or duvet.
- Check the battery compartment: screw-fastened or two separate actions to open.
Sources
- Assurance Maladie (ameli.fr), “Comment bien coucher un bébé ?”, published on 10 October 2024.
- Assurance Maladie (ameli.fr), “Mon enfant a avalé une pile bouton : agir vite”, 20 November 2025.
- Haute Autorité de santé, recommendations on preventing sudden unexpected infant death and on safe sleep, covered in our dedicated article.
