In Sharon's dream world of Harry Barker, a cloaking device is a hacker construct that allows the user to become virtually invisible. Exactly how this object works has not been explained; however, since virtual reality has been proven to be a very effective and prolific tool in the hacker world, one possible explanation is that it uses VR to wrap the user in an "avatar" the essentially displays whatever image is behind them, effectively "bending" light around the user and rendering them invisible. Whether it affects sound, smell, or other sensations has not been mentioned. Cloaking devices are considered very rare and complicated devices, and few known effective examples exist.
In "Harry Barker and the Prisoner of Angband", it was revealed that Harry had been given a cloaking device by a mysterious, anonymous benefactor sometime during his first year at Hollerith's. However, this fact was apparently not relevant until two years later, when Don reminded him of its existence. ("You know, the one you received as a mysterious gift in our first year but which we conveniently forgot about until just now?") Harry was able to use the cloaking device to spy on Patty McDongle and Coreleak Fud as they discussed "Serious" Nick's escape from Angband Prison.
Harry's cloaking device is analogous to the invisibility cloak seen in Harry Potter. (Note, however, that those unfamiliar with the overall Potter story may wish to avoid following that link, as it contains a massive spoiler for the final installment of the series. Whether that becomes a spoiler for future Harry Barker tales remains to be seen.) The cloaking device has long been a staple of science fiction since its introduction in Star Trek in the 1960s.