Shimmer

A Shimmer was a cloaking device used by the Vinvocci to change their appearance.

Appearance and function
These devices were disguised as a wristwatch, and was apparently uncomfortable to use. The Doctor could easily detect a shimmer even when not looking at it, such as when he deactivated Rossiter's shimmer. (DW: The End of Time)

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

Behind the scenes

 * The name of the device implies that the cloaking process involves light.