Sonic gauntlet

A sonic gauntlet was a type of sonic device, one of which was used by Paternoster Gang member Jenny Flint. She wore it on her left arm.

Very soon after a Tyrannosaurus rex was accidentally brought to 1890s London, Jenny used her sonic gauntlet to scan the dinosaur, finding that the creature seemed to have something lodged in its throat; what she was detecting was the Twelfth Doctor's TARDIS. (TV: Deep Breath)

Behind the scenes
Jenny Flint's sonic gauntlet was one of three props (all of which were sonic devices used by the Paternoster Gang) that resulted from a Blue Peter competition. The sonic gauntlet was designed by a thirteen-year-old boy from Somerset named Connor. His design included a tumbler to make locks fall apart, a radioactivity measurer and receiver dish, and a watch that showed the conductivity of metal in a lock. Steven Moffat, who helped judge the competition, commented, "We love this because it looks really cool; it looks quite steam punk – it looks Victorian, but looks technological at the same time and I can just imagine Jenny Flint when she goes out in the morning needing something like that on her arm." In the stage directions from the script of Deep Breath, the device was simply described as Jenny's "hi-tech gauntlet," rather than mentioning it being sonic in nature.