Invisibility watch

From Tardis Wiki, the free Doctor Who reference
The Twelfth Doctor makes use of the invisibility watch. (TV: The Caretaker)
You may be looking for the Doctor's invisible watch.

An invisibility watch granted the wearer the ability to vanish from view. The Twelfth Doctor used one to avoid being scanned by a Skovox Blitzer. Clara Oswald lent it to Danny Pink so he could see how she acted around the Doctor. However, he sensed Pink's presence, foiling the plan. (TV: The Caretaker)