Beard trimmers and body groomers both resemble barbershop hair clippers. Variations in size and attachments comprise the majority of differences between beard trimmers and body groomers, but for some jobs they may be interchangeable.
Beard Trimmer
Beard trimmers tend to be smaller than hair clippers or body groomers, sized to accommodate facial grooming. Attachments make the device adjustable for mustache, goatee, beard, sideburns and even chin stripe trimming and shaping. Beard groomers also come with an attachment that allows the user to create precise lines, allowing expert shaping of facial hair.
Body Groomer
Body groomers often are slightly larger than beard trimmers, with more attachments to accommodate body hair. Most have comb attachments allowing the user to trim body hair without shaving to the skin. Additionally, some brands of body groomers have attachments, making it easier for the user to trim or remove unwanted hair, on his back for example, without requiring a helper.
Comparison
Beard trimmers could be used for some body grooming that is within reach, meaning it would not require the use of attachments to assist in reaching the areas. Body groomers, however, do not come with the same precision shaping attachments that beard trimmers come with, so a body groomer would not be able to do accurate facial hair trimming, shaping or grooming.