"Omega device" was a term sometimes applied to a technological creation of the Time Lord Omega. Davros and the Imperial Daleks referred to the Hand of Omega as the "Omega device." (TV: Remembrance of the Daleks)
Ace later used an Omega device, capable of breaking down the barriers of time, to time lock Skaro in an attempt to remove the Daleks from history, resulting in time being fractured. It was hand-held, could fit in a pocket, and could create a time corridor to pull an individual through time.
Unused to using the device, Ace wound up fracturing Skaro's timeline, causing various travellers to find themselves at the Dalek City in the aftermath of the Thal-Dalek battle. When one Dalek attempted to continue the plan to irradiate Skaro's atmosphere, the Seventh Doctor and Bernice Summerfield summoned a future version of the Dalek, sparking a firefight. The paradox reset the omega device, returning Skaro's timeline to normal. (AUDIO: The Lights of Skaro)