Machine That Goes "Ding"

A Machine That Goes "Ding" was a machine that the Tenth Doctor used to detect Zygon DNA.

Besides lighting up when in the presence of a Zygon, the machine could microwave frozen dinners from up to 20 feet and download comics from the future.

The Doctor thought the machine identified Elizabeth I as a Zygon, but it had in fact detected that her horse was one. (TV: The Day of the Doctor)

Behind the scenes
It resembled the Timey-wimey detector from Blink, being made of a bunch of random objects.