You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
TECHNICAL FIELD 
       [0001]    This invention relates to a lock such as might be used to retain a door in an open or closed position. 
       BACKGROUND TO THE INVENTION 
       [0002]    Locks are commonly used to retain doors or windows or the like in either an open or closed condition. In the case where it is desirable control the lock from a remote location, an electrically operated lock may be used. One form of electrically operated lock is an electromagnetic lock. These typically comprise an armature of ferrous material and an electromagnet. Activation of the electromagnet causes strong magnetic attraction between the armature and electromagnet. It is necessary for current to flow through the electromagnet to maintain the attraction. Deactivation of the electromagnet allows the armature to release from the electromagnet. 
         [0003]    In the case of security doors in commercial premises or the like, electromagnetic locks are sometimes used which require a force of about 2000N to 5000N to break the attraction between the armature and the electromagnet. In order to provide such strong magnetic attraction it is necessary to use a strong electromagnet and a correspondingly large armature. In addition, a current of approximately between 40 mA up to 400 mA must constantly flow through the electromagnet whilst it is retaining the door. 
         [0004]    The following formula shows the general equation determining the electromagnet holding force: 
         [0000]        F=K *( B   g ) 2   *A   
       Where  
       [0005]    F is the holding force in Newton, 
         [0006]    K is the constant, 
         [0007]    B g  is full density of magnetism (Wbm 2 ) 
         [0008]    A is the surface area of the electromagnet (m 2 ) 
         [0009]    It would be advantageous to provide a remotely operable lock with an adequately strong locking action which uses either a smaller amount of raw materials during construction or which uses less electricity during operation than existing locks. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a lock including magnetic lock means and mechanical lock means. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a cross sectional view along the line A-A of  FIG. 2  of a lock according to an embodiment of the present invention; 
           [0013]      FIG. 2  is a cross sectional view of the lock of  FIG. 1  along the line C-C; 
           [0014]      FIG. 3  is a cross sectional view of the lock of  FIG. 2 , but in a position when a force is being exerted upon the door being locked; 
           [0015]      FIG. 4  is a cross section view of the lock of  FIG. 2  along the line B-B and shown affixed to a door in a position when a force is being exerted upon the door; 
           [0016]      FIG. 5  shows the lock in the same view as shown in  FIG. 4 , but in the position shown in  FIG. 3 ; 
           [0017]      FIG. 6  shows an enlarged perspective view of the sleeve of the lock of FIG.  1 ′ 
           [0018]      FIG. 7(   a ) shows a lock according to a second embodiment of the invention; 
           [0019]      FIG. 7(   b ) shows the lock of  FIG. 7(   a ) in another position; and 
           [0020]      FIG. 7(   c ) shows the lock of  FIG. 7(   a ) in yet another position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring to  FIG. 1 , a lock  10  is shown including magnetic lock means in the form of two electromagnets  1  which, when supplied with electric current, are magnetically attracted to armature  2 . 
         [0022]    Lock  10  further includes mechanical lock means including pin  24  which has a groove  26  provided about its shaft. Pin  24  is attached to armature by way of screw thread  25 . 
         [0023]    A hollow sleeve  42  is affixed to backing plate  54  by way of screw  44  and surrounds pin  24 . Six locking elements in the form of generally spherical balls  27  are mounted in sleeve  42 . Each ball  27  sits in a through hole  28  in sleeve  42 . Each through hole  28  narrows slightly at the end nearest the centre of the sleeve. This allows each ball  27  to be inserted into hole  28  from the outside of the sleeve, and each ball is prevented from passing right through the hole  28  by the narrowed portion. 
         [0024]    The electromagnets  1  are connected to a centre piece  4  which carries a shoulder  41 . Electromagnets  1  are mounted to backing plate  54  by way of screws  31  packed with a stack of sprung washers  32 . Centre piece  4  sits between electromagnets  1  and is maintained in a substantially fixed relationship to the electromagnets by way of flanges  12 . Sprung electrical contact fingers  35  bear against flat contacts  11  to provide electrical connections to the electromagnets  1 . 
         [0025]    When electric current is supplied to electromagnets  1  they become attracted to armature  2 . An attempt to open the door whilst the electromagnets are active causes movement of armature  2  along with electromagnets  1  and centre piece  4  in the direction indicated by the bold arrows in  FIG. 1  by way of compression of sprung washers  32  (note compression of washers  32  in  FIG. 3 ). The electromagnets  1 , centrepiece  4  and shoulder  41  move as one to the position shown in  FIG. 3 . The sleeve  42  remains fixed to backing plate  54 . 
         [0026]    Comparing  FIGS. 1 and 3 , in  FIG. 1  balls  27  are out of engagement with groove  26 . However, in  FIG. 3 , movement of shoulder  41  has effected a ramping movement which has guided balls  27  into engagement with groove  26 . Thereafter, increased force applied to the armature in the direction shown by the white arrow in an attempt to open the door is resisted by engagement of balls  27  within groove  26  of pin  24 . Thus, in  FIG. 3  both the magnetic action of electromagnets  1  and the physical engagement of balls  27  and pin  26  simultaneously serve to resist separation of the armature from the electromagnets and thus keep the door closed. 
         [0027]    It has been found that, when compared to locks that rely on electromagnetic attraction alone, locks according to embodiments of the invention can provide the same resistance to opening but use electromagnets of reduced capacity. This means it is possible to use smaller electromagnets and thus use less raw materials to achieve the same strength of lock as in the case of known electromagnetic locks, with a consequential drop in power consumption due to the reduced capacity of the electromagnet. 
         [0028]    Microswitch  33  is configured to detect movement of the electromagnets  1  between the positions shown in  FIGS. 1 and 3 . This allows remote detection of a force being applied to a door that is sufficient to compress sprung washers  32  and may indicate an attempt to force open the door. 
         [0029]    Comparing  FIGS. 4 and 5 , the lock is shown at rest in  FIG. 4  with the lock affixed to doorjamb  102  and armature  2  affixed to door  100 . At  FIG. 5  the lock is shown when a forced attempt is being made to open the door  100 . Note that in  FIG. 5 , balls  27  have been pushed into engagement with groove  26  of pin thus providing mechanical resistance to separation of armature and electromagnets. 
         [0030]    Referring again to  FIG. 1 , when the electromagnets deactivated there is no attraction between the armature  2  and the electromagnets  1 . Thus, if an attempt it made to open the door, the armature easily separates from the electromagnets. Pin  24  is free to release from sleeve  42  as balls  27  are not held in engagement with groove  26  by shoulder  41 . 
         [0031]    Referring to  FIG. 7(   a ), an alternative embodiment of the invention is shown. In this version two microswitches  238 , 239  are used. The microswitches are actuated by the heads of actuation screws  240 ,  241 . The depth of insertion of each of screws  241 ,  240  into plate  224  dictates the force required to actuate either of microswitches  239 ,  240 . 
         [0032]    Referring to  FIG. 7(   b ), a moderate force is being applied to device  200  which is comparable to the force that might be applied by a person attempting to push open a door. The force is balanced by compression of spring  230 . It can be seen that microswitch  239  has become actuated by the head of actuation screw  241 . 
         [0033]    Referring to  FIG. 7(   c ), a large force is being applied to device  200  which is comparable to the force that might be applied by a person attempting to force open a door. The force is balanced by further compression of spring  230 . It can be seen that microswitch  238  has become actuated by the head of actuation screw  240 . 
         [0034]    Device  200  includes a radio transmitter device which can transmit signals indicating a condition of device  200  based on the positions of microswitches  239 ,  240 . If neither switch is actuated then this indicates that the door is not being pushed. 
         [0035]    If switch  239  is actuated then this indicates that somebody may be attempting to open the door. The radio transmitter circuit may transmit a signal indicating this. This may be received at a local unit which sounds an alarm to indicate to the person that the door is locked. 
         [0036]    If switches  239  and  240  are actuated then this indicates that somebody may be making a forced attempt to break open the door. The radio transmitter circuit may transmit a signal indicating this. This may be received at a remote security console or the like to indicate to security personnel that a forced attempt may be being made to open the door to which device  200  is attached. 
         [0037]    In the above described embodiment the lock was described as being used to retain a door in the closed position. Similarly, the lock can be used with windows and other building openings. Similarly, the lock can be used to keep a door or window or the like in the open position. 
         [0038]    The lock described above utilised two electromagnets. Similarly, a greater or lesser number of electromagnets can be used. 
         [0039]    The lock described above utilised one pin which provided a mechanical locking action. Similarly, more than one pin can be used. 
         [0040]    The lock described above included electromagnets that were connected to their power supply by way of sprung finger contacts provided on the backing plate of the lock which made contact with terminals of the electromagnets when the electromagnets were installed in the lock. Similarly, the electromagnets could be hard wired. 
         [0041]    Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated. 
         [0042]    Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.

Summary:
A lock is disclosed including magnetic and mechanical locking features. The mechanical lock means operates in response to an attempt to force open the lock. The mechanical lock means includes a pin and at least one locking element; the mechanical lock means operates by engagement of the at least one locking element with a recess.