with reference to the drawings , wherein like numerals represent like components or assemblies throughout the drawings , a lock system in accordance with the invention is designated generally by the numeral 10 . the lock system 10 secures a door 28 against a door frame 20 . the lock system 10 comprises an electromagnetic lock assembly 12 and an armature assembly 14 . the electromagnetic lock assembly 12 is preferably located at an upper corner of the door frame 20 so as to present minimal obstruction to persons and equipment passing through the doorway . the electromagnetic lock assembly 12 comprises a lock housing 16 . the lock assembly 12 is rigidly fixed to the door frame 20 by a lock mounting plate 22 . ( see fig1 .) the plate 22 is fixed to the door frame 20 by screws 24 extending through the plate 22 and into the door frame 20 . housing end plates 18 at the ends of the lock housing 16 are secured by machine screws . mounting bolts 26 extend through the housing end plates 18 and into the lock mounting plate 22 to securely mount the housing 16 to the door frame 20 . the electromagnet 30 is constructed of a series of stacked e - shaped laminations 32 . an electromagnet coil 34 is positioned inside the spaces defined by the e - shaped laminations 32 . the coil is supported in the spaces by a potting material , or the coil can be wound around a bobbin , with the bobbin held by frictional engagement with the legs of the laminations 32 . the end edges of the legs of the e - shaped laminations 32 define an electromagnetic attractive face 36 on the front of the lock assembly 12 . the defined attractive face 36 is oriented toward the door 28 . the armature assembly 14 is mounted to the door opposite the lock assembly 12 . the armature assembly 14 comprises an armature 38 and an armature mount . the armature 38 is constructed of a ferromagnetic material such as soft iron for strong electromagnetic engagement with the attractive face 36 of the electromagnetic 30 when the electromagnet 30 is energized . an armature backing plate 40 is affixed to the back of the armature 38 by machine screws . the armature 38 and the armature backing plate 40 define an armature cavity 42 of generally cylindrical shape therebetween . the armature backing plate 40 further defines a coaxial bolt opening 43 contiguous with the armature cavity 42 . the bolt opening 43 has a smaller diameter than the corresponding diameter of the armature cavity 42 . an armature bolt 44 is captured within the armature cavity 42 . the armature bolt 44 has a slotted head 46 and a threaded shank 48 . the slotted head 46 is positioned in the armature cavity , and the shank portion 48 extends through the bolt opening 43 and into the door 28 . a blind nut 50 passes through a bore in the door 28 and threadably engages with the threaded shank 48 of the armature bolt 44 to hold the armature bolt 44 in a fixed relation to the door 28 . an armature washer 52 is positioned underneath the slotted head 46 and around the shank 48 of the armature bolt 44 . the diameter of the armature washer 52 is larger than the diameter of the bolt opening 43 in the armature backing plate 40 through which the armature bolt 44 passes so that the slotted head portion 46 of the armature bolt 44 is captured within the armature cavity 42 . the bolt opening 43 in the armature backing plate 40 is sufficiently large , however , having a diameter greater than that of the bolt shank 48 to allow the armature 38 and the armature backing plate 40 to rock on the armature bolt 44 with a constrained motion . to maintain alignment of the armature 38 on the door 28 , armature pins 41 mounted to the armature 38 extend into armature pin bores 45 in the door 28 . the pins 41 maintain alignment of the armature 37 relative to the door 28 when the armature 38 floats . the floating motion is illustrated by comparing the armature positions of fig3 and 4 . an opening 47 is also provided through the armature to in part allow access to the slotted head of the armature bolt . ( see fig4 .) a cap 49 may be snapped in place to cover the head 46 . the constrained motion of the armature assembly 14 serves at least two purposes . first , the constrained motion of the armature assembly 14 allows the armature 38 to fully engage in surface to surface contact with the attractive face 36 of the electromagnet 30 to enhance the bonding qualities of the lock . the limited floating relationship compensates for small discrepancies in position and angle between the armature system 14 and the lock system 12 . naturally , the absence of gaps between the armature 38 and electromagnet 30 facilitates a strong electromagnetic bond between the components and therefore a strong locking force . the constrained movement feature of the armature assembly 14 also accommodates small constrained movement of the door 28 when the armature system and lock system 12 are engaged . this small constrained movement of the door functions as an activating force for triggering a switch mechanism 55 . the constrained movement is permitted by the captured armature bolt and an armature spring 54 . the armature spring 54 is preferably a conical coil spring which assumes a substantially flat configuration in the fully compressed state . the armature spring 54 is positioned between and exerts an expansion force on the armature washer 52 and the armature backing plate 40 . the axial position of the washer 52 is limited by the fixed position of the bolt head 46 in relation to the door and , in the locked configuration of fig2 by the annular wall of the armature cavity 42 . the armature spring 54 thus serves to hold the armature 38 in relatively tight engagement with the door 28 . when the armature system 14 is electromagnetically bonded to the electromagnet 30 , the armature spring 54 biases the door 28 to the fully closed position . ( see fig3 .) however , when a force is placed upon the door 28 to open the door 28 , the armature spring 54 compresses , allowing the door to swing very slightly in an opening direction . ( see fig4 .) the door 28 remains locked however , even when slightly displaced , due to the armature being in continuous and substantially full surface - to - surface engagement with the electromagnet 30 . by selecting an appropriate pre - established spring force for the armature spring 54 , the magnitude of force necessary to overcome the force of the spring and displace the door can be regulated . for example , on doors leading to the exterior of a building , the armature spring 54 may have a higher spring rate to avoid actuating the lock during certain exterior environmental conditions such as wind conditions . secured interior doors , which are not subject to intense transient environmental forces , may employ springs with lower spring rates so as to allow for easier door opening . furthermore , the spring rate of the armature spring 54 can be selected to compensate for doors of different masses , or for an atypical lock location on a particular door . the constrained motion of the armature relative to the door is employed to trigger the switch mechanism 55 . when the armature spring 54 compresses due to a person attempting to use the door 28 , the small motion of the door 28 may actuate the switch mechanism 55 to activate an alarm , begin a delay sequence , or initiate some other security or emergency function , as described below . the switch mechanism 55 , which preferably functions in a bistable mode , comprises a plunger assembly 58 and a control switch 68 . the switch plunger assembly 58 is supported by the walls of a switch plunger passage 56 . the switch plunger passage 56 extends through the center of the electromagnet 30 . ( see fig5 .) the plunger assembly 58 has a plunger head 60 dimensioned and positioned to extend through the opening 47 in the armature and to contact the slotted head 46 or cap 49 of the armature bolt 44 . a plunger rod 62 fixed to the plunger head 60 extends through the plunger passage 56 and terminates beyond the back of the electromagnet 30 . a plunger spring 66 biases the plunger 58 to protrude in front of the attractive face 36 of the electromagnet 30 and toward the armature system 14 . the spring force of plunger spring 66 is much less than that of armature spring 54 . the plunger spring 66 is confined by the wall of the plunger passage 56 and biases against the plunger head 60 . a plunger stop 64 is fixed to the plunger rod 62 behind the electromagnet 30 . the plunger stop 64 limits the distance the plunger head 60 extends in front of the attractive face 36 of the electromagnet 30 when the armature 38 is swung away from the lock assembly 12 . the end of the plunger rod 62 opposite the head contacts the arm of the control switch 68 . the control switch 68 is preferably a microswitch for compactness . the location of the switch mechanism 55 in a central position relative to the electromagnet attractive face provides a compact and efficient configuration for the lock unit . the control switch 68 is mounted to a circuit board 69 which mounts the other electrical and electronic components of the lock assembly 12 . furthermore , when the armature assembly 14 is electromagnetically bonded to the lock assembly 12 , the switch mechanism 55 is well protected . during operation of the electromagnetic lock system 10 of the invention , the door 28 is held in a normally closed position with the armature system 14 electromagnetically bonded to the electromagnet 30 . ( see fig3 .) the switch plunger assembly 58 is retracted into the plunger passage , and the plunger head 60 contacts the slotted head portion 46 of the armature bolt 44 or a cap 49 mounted to the head portion 46 . when a person attempts to pass through the doorway , the person pushes or pulls on the door 28 depending on whether the person is attempting to egress or ingress . due to the constrained motion permitted by the armature system 14 , the door can swing slightly outward away from the door frame ( in the direction of the fig4 arrow ), therefore compressing the armature spring 54 between the armature bolt washer 52 on the armature bolt 44 and the armature back plate 40 . ( see fig4 .) the door 28 is restricted from any further outward displacement due to the armature bolt 44 being captured within the armature cavity 42 , and the armature 38 being bonded to the electromagnet 30 . the constrained or limited displacement of the door 28 is sufficient to move the armature bolt 44 outward away from the attractive face 36 of the electromagnet 30 . the plunger assembly , in contact with the cap 49 through the armature bolt , then also moves outward due to the biasing force of the plunger spring 66 . the displacement of the switch plunger assembly 58 displaces the end of the plunger rod 62 from the control switch 68 . the control switch 68 thus changes from a first state ( fig3 ) to a second state ( fig4 ) to effectively generate a signal . the signal generated by the control switch 68 is transmitted to a lock control system 70 . the lock control system 70 controls the energizing and deenergizing of the electromagnet 30 . in the preferred embodiment of the lock system 10 , the lock control system 70 , on reception of the signal from the control switch 68 , initiates an alarm and begins a delayed unlocking sequence . after the lock control system 70 has counted down for the pre - established delay time , the lock control system 70 deenergizes the electromagnet 30 . this deenergizing of the electromagnet 30 releases the armature system 14 from the electromagnet 30 , and thereby allows the door 28 to swing to a fully open position . the actuation of switch 68 may be employed to accomplish a wide spectrum of functions . in one embodiment of the invention , an attempt to use the door 28 secured by the lock system 10 activates an audible and / or visual alarm 71 at the site of the doorway . the lock control system 70 may also transmit an alarm signal over multi - strand lines 72 to a remote security control panel 74 . either the local or remote alarms could be combined with the delayed egress sequence to allow security or hospital personnel sufficient time to travel to the site of the doorway . furthermore , the lock system 10 can be efficiently integrated into a fire and security system to provide immediate ingress or egress in an emergency situation . the door security system provided by the invention may further comprise a card reader , key pad , contact activatable electronic key or other form of personal identification reader . with reference to fig1 a personal identification reader such as a key pad 76 can be located on the first side of the door 28 . the keypad 76 communicates with the lock control system 70 and / or the remote security control panel 74 . entry of a valid code into the key pad 76 allows an immediate egress and does not activate an alarm . a second reader 78 which also communicates with the lock control system 70 and / or the remote security control panel 74 can be provided on the second side of the door for immediate ingress without an alarm . the programming for such systems is well known and u . s . pat . no . 5 , 065 , 136 frolov et al is incorporated by reference as an example of such a system . the lock control system 70 , readers 76 , 78 and remote security panel 74 communicate over the multi - strand lines 72 . furthermore , the lock system 10 may be powered by a power supply 80 over the lines 72 . while a preferred embodiment of the foregoing invention has been set forth for purposes of illustration , the foregoing description should not be deemed a limitation of the invention herein . accordingly , various modifications , adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention .