semiatic
Hi

Hi on a thermometer (above the measuring range)

The thermometer measured something hotter than the highest temperature it is built to report, so it shows Hi instead of a number. The manuals read treat it as a reading to take again after checking how it was taken, not as a temperature.

Check your thermometer’s manual — makers differ.

What it is for

Measure again, following your manual’s steps; Braun (ThermoScan) and Microlife (NC 200) give the same fix for Hi as for Lo: clean the probe or sensor and take the reading again. Omron’s ET720 manual says: “Use the unit within its measurable range. If a malfunction still exists, please contact OMRON customer service.” About a high temperature itself, Omron’s manual adds: “A high or prolonged fever requires medical attention, especially for small children. Please contact your doctor.”

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 Hi, HI or just H where the number would be. Some makers show a word or an error screen instead.
Names makers use
Hi (Omron ET720); HI (Braun ThermoScan); H (Microlife IR 310, NC 200 and MT 410); Error (Withings Thermo); An error screen (Beurer FT 90 and FT 95, Braun No touch BNT 400)

Where makes differ

The ceiling depends on the maker and the mode. Omron’s ET720 manual shows Hi above 108.0°F (42.2°C) on the forehead and above 176°F (80°C) in surface mode. Braun’s ThermoScan manual shows HI above 42.2 °C (108 °F), and Beurer’s FT 95 manual gives its error above 42.2 °C (108 °F) on the forehead and above 80 °C in object mode. Microlife uses a plain H: its manuals give it above 43 °C on the IR 310 and in body mode on the NC 200, above 42.9 °C on the MT 410 stick thermometer, and above 99.9 °C in the NC 200’s object mode. Withings’ Thermo shows the word Error above 43.2°C (109.76°F). Braun’s No touch BNT 400 uses one message for both ends, shown above 43 °C or below 34 °C.

What it does not mean

Hi is not the fever alarm: the thermometers read here show a fever as a number with a colour or a symbol, and Hi only when the reading is off the scale. It is not AH either, which Microlife’s manuals define as the room being too hot.

Other symbols with the same shapes

LoLo on a thermometer (below the measuring range)The letters Lo, LO or just L where the number would be. Some…ErrErr or Er with a number (thermometer error code)Err, ERR or Er with a number where the reading should be. Braun…M2M, memory number or memory icon (a stored reading)An M, sometimes with a number after it, or a small memory icon…AHALRoom too hot or too cold (AH, AL or ambient message)The letters AH or AL on Microlife thermometers; an error screen…POSPOS, 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:

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