Room too hot or too cold (AH, AL or ambient message)

The room, or the thermometer itself, is outside the temperature range its maker says it can measure accurately in. It is about the air around the thermometer, not the person.

Check your thermometer’s manual — makers differ.

What it is for

Leave the thermometer in the room where you will measure, then try again. Braun (ThermoScan): “Allow the thermometer to remain for 30 minutes in a room” within its range. Microlife (NC 200): “Allow the thermometer to rest in a room for at least 30 minutes”. Omron (ET720): leave the unit within its range “for at least 30 minutes”. Withings says a reading can seem rather high when the thermometer has been stored in a cold room, and to leave it in the patient’s room for 30 minutes.

These pages report what each maker’s manual says and quote it wherever health is involved. They do not diagnose anything, they are not medical advice, and they do not tell you whether a temperature is a fever or what to do about it; only your own thermometer’s manual and your doctor or nurse can do that for the person you are looking after.

What it looks like: The letters AH or AL on Microlife thermometers; an error screen with a thermometer or house on others.
Names makers use: AH and AL (Microlife); Ambient temperature message (Braun ThermoScan, Omron ET720); Room temperature error (Beurer FT 95)

Where makes differ

Operating ranges differ: Braun’s ThermoScan, Omron’s ET720, Microlife’s IR 310 and Withings’ Thermo work from 10 to 40 °C (50 to 104 °F), but Braun’s No touch BNT 400, Beurer’s FT 95 and Microlife’s NC 200 in body mode need at least 15 °C. Microlife’s NC 200 accepts a colder room, down to 5 °C, in object mode. Omron’s ET720 manual shows this error for a rapid change in the room temperature too, not only for a room that is out of range.

What it does not mean

It is not Lo or Hi, and it says nothing about the person’s temperature. It is not the thermometer symbol printed on the box either, which gives the storage limits (see the temperature-limit page).

Other symbols with the same shapes

Lo on a thermometer (below the measuring range)The letters Lo, LO or just L where the number would be. Some…Hi on a thermometer (above the measuring range)The letters Hi, HI or just H where the number would be. Some…Err or Er with a number (thermometer error code)Err, ERR or Er with a number where the reading should be. Braun…Fever colours and fever symbol (green, yellow or red screen)The screen or a light glows green, yellow or red after a reading,…M, memory number or memory icon (a stored reading)An M, sometimes with a number after it, or a small memory icon…POS, ERP or Er 2 (thermometer not held in place)Short letters such as POS or ERP instead of a reading, often with…

Sources

No published standard we could check defines the symbols on a digital thermometer’s display, so this meaning is taken from 5 makers’ own manuals and support pages, each fetched and read on the date shown:

Microlife: Microlife Ear Thermometer IR 310 — instruction manual (IB IR 310 N-V10, revision 2024-09-13, PDF) — Error Messages: Ambient temperature too high «AH» above 40.0 °C / 104.0 °F; too low «AL» below 10.0 °C / 50.0 °F; operating conditions 10 – 40 °C. Checked 2026-09-29.
Microlife: Microlife NC 200 non-contact thermometer — instruction manual (IB NC 200-e N-V10, 2026-08-17, PDF) — Error messages: «AH» above 40.0 °C / 104.0 °F; «AL» below 15.0 °C / 59.0 °F in body mode or 5.0 °C / 41.0 °F in object mode; rest the thermometer in the room for at least 30 minutes. Checked 2026-09-29.
Braun: Braun ThermoScan 7 (IRT 6520) and ThermoScan 3 (IRT 6030) infrared ear thermometers — instruction manual (Asia-Pacific, PDF) — Errors and troubleshooting: “Ambient temperature is not within the allowed operating range (10 – 40 °C or 50 – 104 °F)”; “Allow the thermometer to remain for 30 minutes in a room where the temperature is between 10 and 40 °C”. Checked 2026-09-29.
Braun: Braun No touch + forehead thermometer BNT 400 — instruction manual (Asia-Pacific, PDF) — Errors and troubleshooting: the message also shows “when the room temperature is outside the operating range of 15 °C – 40 °C (59 °F – 104 °F)”. Checked 2026-09-29.
Omron: Omron No-Touch Forehead Thermometer ET720 (MC-720-Z) — instruction manual (US, 5681249-5D, PDF) — The Icons and Error Messages: “The unit is showing a rapid ambient temperature change” and “The ambient temperature is not within the range between 50 and 104°F (10 and 40°C)”; leave it there for at least 30 minutes. Checked 2026-09-29.
Beurer: Beurer FT 95 non-contact thermometer — instructions for use (2021-06-22, PDF) — Error messages: “Room temperature below 15 °C or above 40 °C (<59 °F, >104 °F)”; room temperature must be between 15 °C and 40 °C. Checked 2026-09-29.
Withings: Withings Thermo — regulatory information and troubleshooting (PDF) — Troubleshooting: “The temperature seems rather high — The unit has been stored in a cold room — Leave the unit in the room where is the patient for 30 minutes”; operating temperature 10°C – 40°C. Checked 2026-09-29.

Written in our own words; quotations are the makers’ wording.