Unlike old-fashioned models, digital thermometers don't contain mercury. Rather, digital models are powered by a small battery and display temperatures on a small screen.
Modern digital thermometers can take readings in several ways: oral, rectal, tympanic (ear), forehead and axillary (underarm). Oral and rectal readings are the most common methods. Tympanic digital thermometers, while convenient for children and not as invasive, can be problematic, because improper insertion in the ear canal can result in an inaccurate reading.
There are also some niche products out there. Pacifier digital thermometers, for instance, take readings through a probe in the pacifier nipple. Most reviewers say these thermometers do take accurate temperatures -- but many users report that their child is unable to continuously keep the product in their mouth for a correct reading (a process that typically takes at least 90 seconds).
You can find all sorts of fancy features on more expensive digital thermometers, but experts say you don't really need to spend a lot to get an accurate thermometer. We found good reviews for models in the $15 to $25 range. When choosing a digital thermometer, here are a few factors to consider: