Digital hygrometers measure both humidity and temperature to give you an idea of the relative humidity. Relative humidity is a value that communicates more accurately how hot or cold you "feel," rather than the exact heat or coldness of the air. Homes, offices, museums, factories, and greenhouses can all use small, handheld hygrometers to monitor their environments.
You can read the temperature and humidity off an LCD readout screen on digital hygrometers. In your household, you might use digital hygrometers in certain rooms to monitor the use of an air conditioner, heater, fireplace, humidifier, or dehumidifier. This way, you can keep your home's temperature around 70° F (21° C), which is comfortable for most people, and your humidity around 47%.
Many people use hygrometers to keep track of the humidity inside their home. Both air conditioners and heaters can sap moisture from the air. It can be harmful to your mucous membranes if the humidity drops below 30%. Then again, getting too much moisture in the air, as in tropical climates, can create condensation and dampness. This might breed mold and mildew, which cause allergies. Ideally, humidity in your home should not get higher than around 60%.
Digital hygrometers have great features to make them more accommodating. They run on batteries, so they are lightweight and easy to carry. For visibility in the dark, you can find some models with illuminated screens. Others have special added features, like a magnetic or adhesive backing for sticking to a wall or cabinet. Digital hygrometers do not need to be independently calibrated, and usually function within an error of 1-3%, depending on the brand's quality.
There are many industrial applications for hygrometers, as well. Cigar enthusiasts put them inside humidors to make sure their cigars are stored under optimal conditions. Lumber workers dry wood that is maintained using digital hygrometers dispersed throughout the kiln. A special collections library may also use these detectors to make sure antique books are kept cool and dry.