Modern digital thermometers are quick, safe and accurate
Almost everybody has had their mother lay her hand on their forehead to diagnose a possible fever -- right? But as accurate as most motherly instincts are, a thermometer is the only way to be truly certain whether you or your child is running a fever. Once upon a time that meant shaking a glass thermometer until the mercury inside settled to the bottom, then holding it in place for up to four minutes in order to get an accurate reading, but today's digital thermometers are faster, safer than and just as accurate as their mercury counterparts.
All thermometers are made to gauge temperatures at one or more sites on the body. They may be designed for taking readings in the mouth, rectum or underarm, with disposable tip covers to reduce the risk of cross-contamination when used on different sites or multiple people. Thermometers that use infrared technology can also be used to take readings from the ear or forehead.
Common user-friendly features include waterproof or water-resistant housings for easy cleaning, a beep to let you know the reading is complete, an illuminated display that changes color to signify elevated or dangerously high temperatures, and the ability to store past readings for easy reference.
In theory, most of the thermometers on today's market are pretty much equal -- but some temperature-taking sites are more useful or challenging than others when it comes to taking accurate temperatures, especially if you're working with a child.
Types of digital thermometers
Oral thermometers are usually very accurate, especially for adults and older children who can place them properly and hold still for the 30 seconds or longer that many thermometers require to get an accurate reading. Another upside is that most oral thermometers can be used for taking axillary/underarm readings and rectal readings too, although, for obvious reasons, you should use disposable probe covers when doing so as well as cleaning the thermometer probe after each use.
Rectal thermometers are highly accurate, making them a good choice for infants and babies who are too young to hold an oral thermometer. They are usually only recommended for use on children under three years old, and the child may start to protest its use long before they have the ability to hold still for the required time to take an oral reading. One alternative is switching to an underarm reading -- in fact, some rectal thermometers can be used for this too, so finding one that does double duty increases the thermometers value.
Ear and temporal (forehead) thermometers, when used correctly, can be just as accurate as oral and rectal thermometers and far less invasive. They're also very quick, usually taking 10 seconds or less to render a reading. This makes them especially popular with parents. That said, they've also been the subject of some controversy regarding their accuracy, which depends entirely on your getting the thermometer into the proper position.
How we found the best digital thermometers
We found a couple of helpful expert roundups of digital thermometers at ConsumerReports.org and TheNightLight.com offer, both of which did extensive testing. Beyond that we paid special attention to user reviews of how the digital thermometers functioned in real-world conditions, which included squirmy babies, fussy toddlers and sometimes recalcitrant adults too.
Digital thermometers aren't the only home health tools that must be accurate, reliable and easy to use. We've also weighted heavily for real-world performance in our reports on blood glucose meters and blood pressure monitors.
The best digital thermometers
It's hard to find fault with the simple, versatile design of an inexpensive basic digital thermometer. In fact, most experts say that unless you're dealing with a small child who can't hold an oral thermometer in the right position for long enough to get an accurate reading, this is all you need. A good, basic digital thermometer can give years of accurate, reliable readings at very little cost.
With that in mind, our Best Reviewed digital thermometer is the Generation Guard Clinical Digital Thermometer (Est. $20). Although some users miss having a backlight on this thermometer, they love its quick, accurate readings (usually in 15 seconds or less, compared to 60 seconds for some of the competition) and appreciate the fully waterproof housing, which lets you wash the entire thermometer if need be.
This Generation Guard thermometer takes a single LR41 battery and can be used for oral, underarm and rectal readings, although it's best suited to oral readings. Underarm readings can be affected by skin temperature, and although the Generation Guard's soft, flexible tip and washability make it ideal for rectal readings, it lacks the broad base that'd eliminate any risk of accidentally inserting it too far.
The Generation Guard thermometer is accurate to 0.2F or 0.1C and it's easy to switch between Fahrenheit and Celsius by holding down the power button. Its features are simple but useful -- it'll beep quietly to tell you when a reading is complete, then display the last reading taken when you turn it on. Finally, it's subject to a "no questions asked" 30-day money back guarantee.
If all you want is a basic thermometer for occasional use or as a backup to your usual thermometer, consider the Vicks V966 Comfort Flex (Est. $10), which costs about half as much as the Generation Guard. Users generally love this thermometer's features, which include a fully waterproof casing, recall of the last temperature taken, and a backlit display that changes color according to the temperature reading.
The Vicks V966F is also fast -- returning results in about eight seconds. However, it only received "fair" ratings for its accuracy and repeatability in one test from a major consumer advocate organization, and it draws enough user concerns about durability and accuracy that we can't award it best-reviewed status. It is, however, a good bargain if you're looking for a simple thermometer for occasional use.
Although simple, functional digital thermometers are more accurate and widely available than ever, a few manufacturers are heading in the opposite direction, creating digital thermometers that sync with your smartphone to enable advanced functions.
The best of these, the Kinsa Smart Thermometer (Est. $18), is priced to be competitive with higher-end basic thermometers. It plugs into your mobile device's earphone jack -- with or without an optional extension cord -- and harnesses your smartphone's power to do most of the processing.
The result is a light, durable device can be used orally, under the arm or rectally, and returns results in about 10 seconds. Users are very happy with the Kinsa Smart Thermometer's accuracy, but it's the companion app that they really love. The free app lets you track symptoms, chart temperature readings over time, and note medications taken. You can even add photos to track conditions like a rash or sore throat. The biggest hit of all, though, is the "bubble game" that helps keep small children entertained and quiet as you take their temperature. They can count or pop the bubbles that appear on the screen.
The Kinsa app also lets you store tracking information for multiple people, and a late-2015 update enabled group tracking, which uses anonymized information from other Kinsa users to let you know if there's an illness circulating in your area. All of the above are roundly praised by user reviewers, and Kinsa's proactive, helpful customer service department gets lots of kudos too.
Elsewhere in this report:
Best Rectal/Ear Thermometers | Best Temporal Thermometers | Buying Guide | Our Sources