A battery operated hair or beard clipper allows you to do diy grooming at home. No need for a trip to the hair dresser when you can do it in your own home.
Beard trimmers have different attachments or an adjustment switch to determine the length of the cut. You can have the short and tidy look or the more rugged longer beard look.
Hair clippers allow home tidy up and again are adjustable for different lengths of cut.
More frequently they are rechargeable but still they can be mains operated.
Many models available can be cleaned by rinsing the cutting head under running water. This will keep the clipper clean and hygienic.