A door strike for captivating and releasing a door bolt, comprising a) a longitudinally elongated carrier, b) a mechanism including a longitudinally elongated solenoid supported by the carrier, the solenoid having a longitudinally movable plunger including a tapered cam surface, c) a trip lever pivotally supported in or on the carrier, d) a laterally extending actuating arm pivotally supported in or on the carrier to be pivoted by the movement of said tapered cam surface as the plunger moves longitudinally in response to solenoid energization, thereby to pivot the trip lever, e) two generally longitudinally extending blocking arms (27, 28) pivotally supported in or on the carrier to be released for pivoting when the trip lever is pivoted, and f) two door bolt retainers (34, 35) pivotally supported in or on the carrier and operationally engaged by the blocking arms (27, 28), respectively with them to be released for pivoting when the trip lever is pivoted, g) said mechanism having an adjusted fail secure first configuration whereby when electrical power to the solenoid is OFF, the mechanism is locked, preventing release of the door bolt for door opening, h) said mechanism having an adjusted fail safe second configuration wherein when electrical power to the solenoid is ON, the mechanism is locked, and when electrical power to the solenoid is OFF, the mechanism is unlocked, releasing the door bolt for door opening, and i) and wherein said mechanism includes a slide link connected to the plunger and movable longitudinally with the plunger and a tab on said link movable by the link between a first position registered with the trip lever and effecting blocking thereof, and a second position wherein the tab is not registered with the trip lever, and when electrical power to the solenoid is OFF, then in said first configuration the tab is in the first position and in said second configuration the tab is in the second position. a) a longitudinally elongated carrier, b) a mechanism including a longitudinally elongated solenoid supported by the carrier, the solenoid having a longitudinally movable plunger including a tapered cam surface, c) a trip lever pivotally supported in or on the carrier, d) a laterally extending actuating arm pivotally supported in or on the carrier to be pivoted by the movement of said tapered cam surface as the plunger moves longitudinally in response to solenoid energization, thereby to pivot the trip lever, e) two generally longitudinally extending blocking arms (27, 28) pivotally supported in or on the carrier to be released for pivoting when the trip lever is pivoted, and f) two door bolt retainers (34, 35) pivotally supported in or on the carrier and operationally engaged by the blocking arms (27, 28), respectively with them to be released for pivoting when the trip lever is pivoted, g) said mechanism having an adjusted fail secure first configuration whereby when electrical power to the solenoid is OFF, the mechanism is locked, preventing release of the door bolt for door opening, h) said mechanism having an adjusted fail safe second configuration wherein when electrical power to the solenoid is ON, the mechanism is locked, and when electrical power to the solenoid is OFF, the mechanism is unlocked, releasing the door bolt for door opening, and i) and wherein said mechanism includes a slide link connected to the plunger and movable longitudinally with the plunger and a tab on said link movable by the link between a first position registered with the trip lever and effecting blocking thereof, and a second position wherein the tab is not registered with the trip lever, and when electrical power to the solenoid is OFF, then in said first configuration the tab is in the first position and in said second configuration the tab is in the second position.