Shimmer

A shimmer was a cloaking device that allowed its owner to change their appearance. The Eleventh Doctor once described it as "an all-in-one disguise kit for aliens that don't look human". (TV: The End of Time, COMIC: Ripper's Curse)

Appearance and function
Shimmer devices used by Vinvocci were disguised as wristwatches, which allowed them to avoid suspicion. While very effective, they were apparently uncomfortable to use. The Tenth Doctor could easily detect such a shimmer even when not looking directly at it, as he did when he deactivated Rossiter's shimmer. (TV: The End of Time)

History
Jack Harkness used a shimmer to adopt a disguise as he met himself from the past when he was still a Time Agent by the name Javic Piotr Thane. Taking it from his future self, Javic used it to assume the form of fellow agent Krim Pollensa to make the Council believe he was dead, and later Maglin Shank as he taunted her and the Council. (AUDIO: Month 25)

Mac'atyde, better known as serial killer Jack the Ripper, used a shimmer suit to disguise himself as human and lure his victims. (COMIC: Ripper's Curse)

Rossiter and Addams picked up a signal from a piece of medical equipment and used shimmers to work undetected for Joshua Naismith. The Doctor deactivated them with his sonic screwdriver. (TV: The End of Time)

On St Valentine's Day 2013, an Ameteli used a shimmer to disguise himself as Cupid. (COMIC: Love is in the Air)

Charles Abbott, a popular writer of spooky children books, was an alien using a shimmer to pretend to be a human. (COMIC: Shock Horror)