A door strike for captivating and releasing a door bolt, the door strike comprising: a) a longitudinally elongated carrier; b) a mechanism including a longitudinally elongated solenoid (17, 170) supported by the carrier, the solenoid (17, 170) having a longitudinally movable plunger (18, 180); c) a slider link connected to said plunger (18, 180) and movable by said plunger (18, 180), wherein said slider link includes a tab; d) a trip lever pivotally supported in or on the carrier and registrable with said tab, wherein when said tab is in a first position, said tab is registered with said trip lever, and when said tab is in a second position, said tab is not registered with said trip lever; e) a laterally extending actuating arm pivotally supported in or on the carrier to be pivoted as the plunger (18, 180) moves longitudinally in response to solenoid energization, thereby to pivot the trip lever; f) a generally longitudinally extending blocking arm (27, 28) or arms pivotally supported in or on the carrier to be released for pivoting when the trip lever is pivoted; and g) a door bolt retainer (34, 35) or retainers pivotally supported in or on the carrier to be released for pivoting when the blocking arm (27, 28) or arms are released for pivoting, thereby to release the door bolt from captivation, for movement with a door; h) said mechanism having an adjusted fail secure first configuration whereby when electrical power to the solenoid (17, 170) is OFF, said tab is in said first position and the mechanism is locked, preventing release of the door bolt for door opening; i) said mechanism having an adjusted fail safe second configuration whereby when electrical power to the solenoid (17, 170) is ON, said tab is in said first position and the mechanism is locked, and when electrical power to the solenoid (17, 170) is OFF, said tab is in said second position and the mechanism is unlocked, releasing the door bolt for door opening; j) and wherein there are first and second spring elements (160, 161) having positions for sequentially resisting plunger axial movement, in a first longitudinal direction, whereby the first element and the second element resist said plunger movement, said spring elements (160, 161) spaced apart longitudinally in the direction of plunger movement. a) a longitudinally elongated carrier; b) a mechanism including a longitudinally elongated solenoid (17, 170) supported by the carrier, the solenoid (17, 170) having a longitudinally movable plunger (18, 180); c) a slider link connected to said plunger (18, 180) and movable by said plunger (18, 180), wherein said slider link includes a tab; d) a trip lever pivotally supported in or on the carrier and registrable with said tab, wherein when said tab is in a first position, said tab is registered with said trip lever, and when said tab is in a second position, said tab is not registered with said trip lever; e) a laterally extending actuating arm pivotally supported in or on the carrier to be pivoted as the plunger (18, 180) moves longitudinally in response to solenoid energization, thereby to pivot the trip lever; f) a generally longitudinally extending blocking arm (27, 28) or arms pivotally supported in or on the carrier to be released for pivoting when the trip lever is pivoted; and g) a door bolt retainer (34, 35) or retainers pivotally supported in or on the carrier to be released for pivoting when the blocking arm (27, 28) or arms are released for pivoting, thereby to release the door bolt from captivation, for movement with a door; h) said mechanism having an adjusted fail secure first configuration whereby when electrical power to the solenoid (17, 170) is OFF, said tab is in said first position and the mechanism is locked, preventing release of the door bolt for door opening; i) said mechanism having an adjusted fail safe second configuration whereby when electrical power to the solenoid (17, 170) is ON, said tab is in said first position and the mechanism is locked, and when electrical power to the solenoid (17, 170) is OFF, said tab is in said second position and the mechanism is unlocked, releasing the door bolt for door opening; j) and wherein there are first and second spring elements (160, 161) having positions for sequentially resisting plunger axial movement, in a first longitudinal direction, whereby the first element and the second element resist said plunger movement, said spring elements (160, 161) spaced apart longitudinally in the direction of plunger movement.