A raised temperature is a telltale sign of illness, so having a thermometer around (with a working battery) is useful, particularly if you're older or have underlying health conditions.
We've tested a number of thermometers which are suitable for babies through to adults (even ones marketed specifically for infants can typically be used by adults).
Our thermometer reviews also assess accuracy and how easy they are to use.
We've concluded that each type – digital probe, ear (tympanic) and forehead (temporal) – has its pros and cons. What constitutes a fever does depend on a number of factors, including your age, the environment, and the type of thermometer you're using. Even having a hot drink before taking your temperature can have an effect on a reading, so make sure you follow the instructions.
Digital probe thermometers are accurate and cheap, but can take a couple of minutes to get a reading.
These are suitable for oral, armpit or rectal readings.
A digital probe thermometer is relatively cheap (around $10–$20) and accurate. Our testing, using a calibrated thermal bath for comparison, shows they're often accurate to within 0.1°C.
Some may take a couple of minutes for armpit (axillary) readings, which makes them less suitable for a restless baby or child. Adults should be able to conduct oral or armpit testing on themselves relatively easily.
Ear thermometers are quick and handy but you'll need to buy disposable sleeves as well.
Costing from $20 to $120, these are placed in the ear canal and use infrared rays to read the body's core temperature. While they can be accurate to within 0.2°C, using them on yourself could be tricky, so ensure you follow the manufacturer's instructions. The temperature of the ambient environment (whether it's too hot or cold) could also affect accuracy.
They usually require you to put a disposable hygienic sleeve or lens filter over the thermometer probe, which will cost extra. The cover keeps the probe tip clean and intact, and also helps prevent infection from one patient to the next.
Ear thermometers may be unsuitable for very small babies under 3–6 months (even up to 12 months), or for the elderly, so do consult the instructions before use. The ear probe covers may also be a choking hazard for small children.
Although less accurate than a digital probe thermometer, a forehead thermometer could be a hygienic option for a busy household.
Costing from around $40 to $100, these use an infrared scanner to measure the forehead's temporal artery. Results are quick (one to three seconds), though generally not as accurate as a digital probe thermometer due to sweat, skin colour or even if you're wearing make-up.
Some are non-contact varieties (held away from the skin), which could limit the spread of germs, making them suitable for a large household where a number of temperatures are regularly being taken as the device can easily be shared.
When used correctly they are accurate to within 0.2°C.
Important note: Many personal thermometers use button batteries, which are very dangerous if swallowed. The back should be secured with a screw (we don't recommend personal thermometers with accessible button batteries). Regardless of design, always keep the thermometer out of a child's reach.
While the probe, ear and forehead types are the most common, other types of thermometers include temperature strips (a plastic strip with heat-sensitive crystals that change colour to give a reading, but are not very accurate), and 'combination' thermometers, which include multiple functions such as ear and forehead or touchless/contact modes.
What happened to mercury thermometers?
You won't find older mercury thermometers on store shelves due to safety concerns. Older alcohol thermometers (with a red indicator) are also generally not available. Although mercury thermometers are still considered very accurate, you shouldn't use them as the fumes are very toxic if the glass is broken and the mercury escapes. They're also more difficult to read.
Mercury thermometers are still sold in Australia by specialist medical suppliers but have been banned in the US and Europe. If you're still using one and it breaks, follow the NSW Government's clean-up instructions.
A temperature of 38°C or more is usually a clear sign of fever, but a slightly elevated temperature might also be cause for concern, depending on where you've measured it, because different parts of the body are slightly different temperatures.
For example, your:
- ear temperature can be higher than your oral temperature (subtract 0.3°C–0.6°C to get the oral equivalent)
- armpit and forehead temperature can be lower than your oral temperature (add 0.3°C–0.6°C to get the oral equivalent).
To further complicate things, we've discovered in our testing that some thermometers automatically convert the temperature taken from other parts of your body to an oral equivalent, and the instructions don't always make this clear.
However, the World Health Organization advises people with even a low-grade fever of 37.3°C or more to self-isolate, to be on the safe side. And if you're feeling unwell, seek medical advice.
As for taking your temperature, always take it in the same way (including, for example the same ear) and ideally at the same time each day, as body temperatures tend to rise a little from morning to evening.
CHOICE tip: It's a good idea to know what your typical healthy 'baseline' temperature is, as everyone is different (you'd have to work this out while you're well).
Our baby thermometer buying guide has a range of relevant tips about useful features which are appropriate for adults. Common things to consider are a large, easy to read display with a backlight for nighttime readings, fever alerts and memory recall functions.
Stock images: Getty, unless otherwise stated.