In Star Trek: The Next Generation, "Transfigurations," the Enterprise was intercepted by "Sudan," a Zalkonian tracking down "John Doe," the mutating Zalkonian. When Picard questioned Sudan's motives even after Sudan demanded John be turned over, he is seen on the viewscreen giving one of his crew members a look. Soon, the entire crew of the Enterprise, except for John Doe, starts suffocating.
Wikipedia's summary says this:
Captain Picard considers the situation, but refuses to release John to the Zalkonians without more information as to the charges. He contacts the other ship and mentions John's strange powers, which alarms Captain Sunad. Sunad immediately triggers a device which causes the entire Enterprise crew to become unable to breathe. John resists the device and heals everyone aboard the Enterprise with one bright flash of his energy.
So here, it's "a device," but how is there any mention of this later on? What is this device or system?