What do Lo, Hi, Err and the other symbols on a digital thermometer mean?
Find it by its shape. 1. Pick what you see on the thermometer’s screen. 2. Match the drawing. Each symbol here is backed by the manuals of at least two different maker groups (Braun, Omron, Microlife, Beurer, Withings), and every fever threshold, every temperature and every piece of health wording is quoted with the name of the maker that printed it.
Check your thermometer’s manual — makers differ.
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.
Tap a shape — the symbols that use it appear here.
Letters — 6 symbols
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…M, memory number or memory icon (a stored reading)An M, sometimes with a number after it, or a small memory icon…Room too hot or too cold (AH, AL or ambient message)The letters AH or AL on Microlife thermometers; an error screen…POS, ERP or Er 2 (thermometer not held in place)Short letters such as POS or ERP instead of a reading, often with…
°C or °F — 2 symbols
Battery — 1 symbol
Coloured screen or light — 2 symbols
Head, object or room — 1 symbol
Probe or cover — 2 symbols
Thermometer or house — 2 symbols
Before you trust any chart, including this one
No published standard we could check defines what a thermometer’s display shows. ISO 80601-2-56, the international standard for clinical thermometers, sets accuracy and safety requirements and is sold rather than published free, so we could not check what, if anything, it says about display symbols. Every meaning on these pages is taken from makers’ own manuals.
- Lo and Hi are not readings. They mean the thermometer measured outside what it can report, and the edges differ: Omron’s ET720 and Braun’s ThermoScan manuals put Lo below 34.0 °C and Hi above 42.2 °C, while Microlife’s IR 310 ear thermometer shows L below 32 °C and H above 43 °C.
- The same letter can mean different things. On a Microlife MT 410 stick thermometer, an L with a flashing °C before you start is normal: Microlife says it means the air is colder than the thermometer’s range and the thermometer is ready. On Microlife thermometers AH and AL are about the room, not the person.
- Flashing does not always mean ready. On Microlife’s ear and forehead thermometers a flashing °C or °F means ready; on its stick thermometer it means still measuring; on Beurer’s forehead thermometers the forehead symbol flashes until the thermometer is ready.
- Fever colours use each maker’s own threshold: Microlife turns the screen red at 37.5 °C, Beurer’s FT 95 turns red over 38 °C, and Braun’s AgeSmart screen moves its thresholds with the age you select. The fever page quotes each one with its maker’s name.
- Some thermometers measure objects and rooms as well as people. Omron’s ET720 manual says that after a minute without use it switches to room temperature mode and keeps the room temperature on the screen, so a number there is not always a person’s temperature.
Maker by maker
- Braun (Kaz, a Helen of Troy company). Braun thermometers are made under licence by Kaz, part of Helen of Troy, which also makes Vicks thermometers, so Braun and Vicks count as one maker group here. Two Asia-Pacific manuals were read from Braun Healthcare’s own download page: the ThermoScan 7 (IRT 6520) ear thermometer, with its AgeSmart green, yellow and red screen, and the No touch + forehead BNT 400. Braun’s US site answered our requests with a bot check (HTTP 403) on 2026-09-29, so its US editions are not cited.
- Omron. The US instruction manual for the ET720 No-Touch Forehead Thermometer (MC-720-Z) was read. Its screen writes Hi and Lo in letters and has forehead, surface and room temperature modes, a memory icon, a mute icon and a battery icon. It has no fever colour.
- Microlife. Three manuals were read: the IR 310 ear thermometer, the NC 200 non-contact thermometer and the MT 410 stick thermometer. Microlife writes single letters and short codes (H, L, AH, AL, ERP, ERR, Er 2) and uses a red backlight for its fever alarm.
- Beurer. The instructions for the FT 90 and FT 95 non-contact thermometers were read, in their June 2021 editions. Beurer prints its error messages as pictures of the screen rather than as text, so these pages describe what each Beurer message means without claiming its exact characters.
- Withings. The Withings Thermo user guide (v2.0, April 2018) and its regulatory information sheet were read. The Thermo shows the word Error both for a reading out of range and for a system fault, and has a coloured fever LED that depends on the age range of the person measured.
- Exergen. Only Exergen’s professional TemporalScanner TAT-2000 manual turned up on exergen.com, not a home model’s, so nothing on these pages is sourced to Exergen.
Related pages
What these pages cannot do
- They do not identify a specific digital thermometer model. They say what a symbol means on the makes cited (Beurer, Braun, Microlife, Omron, Withings); your model’s manual gives the exact measuring range, fever threshold, memory size and codes.
- They cannot tell you whether a temperature is a fever or what to do about it. Every maker cited tells you to consult a doctor in its own words; where a page quotes that, it names the maker.
- They do not cover glass or mercury thermometers, wearable patches, or the screens of the makers’ phone apps.
- They cannot check your thermometer’s accuracy. Microlife, for one, recommends having the MT 410 tested every two years or after it has been dropped.
- Left out: Mute or silent-mode icon. Omron and Braun both show one, but it only says the beeper is switched off and nothing about the reading; your manual shows how to switch the sound back on.
- Left out: Bluetooth, sync and date/time icons. They say whether the thermometer is talking to a phone app or which clock setting is being changed, not anything about the temperature; each maker’s app help explains them.
- Left out: Clean-me reminder. Only one maker’s ear thermometers among those we looked at remind you to clean the probe on screen, so there is no second maker group to confirm it.
- Left out: Vicks thermometers. Vicks thermometers come from Kaz, the same Helen of Troy group as Braun’s, so their manuals would not add a second maker group; we did not read them.
- Left out: Marks printed on the thermometer and its box (type BF, read the instructions, storage temperature limit, keep dry). They are standard medical-device symbols that already have their own pages on this site, linked under Related pages above, so they are not repeated here.
Sources
Every document below is a maker’s own manual or support page, fetched and read on the date shown. Each symbol page quotes what its sources show.
- Omron: Omron No-Touch Forehead Thermometer ET720 (MC-720-Z) — instruction manual (US, 5681249-5D, PDF) Checked 2026-09-29.
- Braun: Braun ThermoScan 7 (IRT 6520) and ThermoScan 3 (IRT 6030) infrared ear thermometers — instruction manual (Asia-Pacific, PDF) Checked 2026-09-29.
- Microlife: Microlife NC 200 non-contact thermometer — instruction manual (IB NC 200-e N-V10, 2026-08-17, PDF) Checked 2026-09-29.
- Microlife: Microlife MT 410 digital stick thermometer — instruction manual (IB MT 410, revision 2025-07-03, PDF) Checked 2026-09-29.
- Microlife: Microlife Ear Thermometer IR 310 — instruction manual (IB IR 310 N-V10, revision 2024-09-13, PDF) Checked 2026-09-29.
- Beurer: Beurer FT 95 non-contact thermometer — instructions for use (2021-06-22, PDF) Checked 2026-09-29.
- Withings: Withings Thermo — regulatory information and troubleshooting (PDF) Checked 2026-09-29.
- Braun: Braun No touch + forehead thermometer BNT 400 — instruction manual (Asia-Pacific, PDF) Checked 2026-09-29.
- Beurer: Beurer FT 90 non-contact clinical thermometer — instructions for use (2021-06-22, PDF) Checked 2026-09-29.
- Withings: Withings Thermo — user guide (v2.0, April 2018, PDF) Checked 2026-09-29.