A deactivation switch, or off switch, was a component of Soong-type androids. Located in the small of the back, this switch could be activated by a press of the fingers. Paired with the switch were a number of small projections. These projections, as Data defined them, were "an android alarm clock". They measured the time this type of android remained unconscious. If the switch was repeatedly pressed, as happened to Data by Lore, the android could appear he suffered from seizures.
On or about Stardate 45208, Doctor Beverly Crusher, under the influence of a mind control device which resembled a kind of futuristic video game but was actually part of an attempt by the Ktarian people to take over the Federation, used the deactivation switch to incapacitate Data because she and her cohorts knew that Data would be immune to the effects of the game. (TNG: "The Game")