Security system for safes
This invention relates to security systems for safes and more particularly to an arrangement for indelible marking of currency within the safe when unauthorized entry is attempted. 
     BACKGROUND ART 
     To deter unauthorized entry to safes time locks have been installed which prevent withdrawal of the locking bolt before expiry of a predetermined time interval. U.S. Pat. Nos. 3,702,451 (Blizard) and 2,140,698 (Goehring) are examples of such devices which ensure that the door cannot be opened except during a permissive time interval following a time delay period which begins with correct setting of the lock tumblers. In neither instance is any special provision included to guard against forcible entry. For the convenient of authorized users of the safe the time period should not be long, but curtailment of the time interval often only delays burglary and does not prevent it. 
     Various types of combination, or key, lock and gas or dye alarm devices have also been developed with varying degrees of success. In most instances these devices have attempted to thwart forcible entry of a safe by a burglar. A guard against forcible entry has been independently provided according to U.S. Pat. No. 3,500,771 (Fisher et al) where a dye or gas cartridge is activated by a sprung firing pin when an access door of a cabinet or vending machine is forced. An interlock between a lock switch and an alarm device has also been proposed by U.S. Pat. No. 1,743,667 (Gill). In this instance a reservoir of a marking fluid is disposed at the top of the safe which is sprayed on to the safe contents dependent upon two separate controls, viz. the position of the safe door and in response to a time mechanism. Release of the liquid occurs when the door is opened except during the time that the time mechanism operates which commences upon correct operation of a combination lock. 
     However, the increasing incidence of safe burglary in banks and other staff-attended establishments has led to coercion of the staff in gaining entry to the safe. In most instances for the safety of the staff, they are advised to cooperate if threatened. 
     It is the principal objection of this invention to provide a security system for a safe which is secure against forcible entry and includes interlocked procedures in sequential operation for permissive access. 
     DISCLOSURE OF INVENTION 
     The invention in one general form consists of a security system for a safe comprising a delayed action time lock permitting unlocking of the safe after a first time period and within a second time period, a switch operable when a door to the safe is opened, a device for dye marking of the safe&#39;s contents and being electrically actuated by said door switch, a key operated switch, and an electrical interlock circuit between the key switch, the door switch and the time lock ensuring that said marking device is not actuated if said key switch is operated before said door switch. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be described in more detail with reference to the accompanying drawings, in which: 
     FIG. 1 is a front perspective of a safe incorporating the security system of this invention; 
     FIG. 2 shows in rear perspective the door of the safe shown in FIG. 1; and 
     FIG. 3 shows by schematic diagram the electrical interlock circuit of the security system. 
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     A safe (4) is shown in FIG. 1 which is generally of conventional form, having a front access door (5) and a safety deposit slot (6) at its top (7). Through a face panel (8) upon the door (5) the forward end of two key switches (9) and (10) protrude from the inside of the door. Key switch (9) has a key slot (11) to accept a first security key (not shown) while switch (10) accepts a second security key (not shown) in its key slot (12). Preferably, a further security key is made available for insertion into slot (12) to enable withdrawal of the cylinder lock from switch (10) shoudld a key change be desired. LED visual indicators (13) and (14) are positioned adjacent respective switches (9) and (10). 
     The operative mechanisms of the key switches (9) and (10) are accessible from the inside of the door (5) (FIG. 2), switch (9) incorporating electrical contacts which are closed with switch operation and connected to terminals (15) and (16), and switch (10) performing the following functions: upon key operation a clockwork timer commences to function and at completion of a predetermined time period first contacts (17) close and at completion of a second time period these contacts open. A second set of contacts (18) close upon key operation and open at completion of the second time period. A locking bolt (19) will be withdrawn to allow the door to be opened, should the key of the time lock be turned during the second time period. An explosive dye marker device (20) incorporating a detonator is mounted upon the inside of the door (5) and activated from the PCB (21). Dry cell batteries (22) are also provided to energize the circuitry, and electrical access to the LED&#39;s (13) and (14) is gained from the inside of the door. A door microswitch (23) has contacts which close when the door is open. 
     Detailed circuitry of the electrical interlock circuit is shown in FIG. 3. The principal components of the circuit comprise a four element NOR gate, two elements, NOR 1 and NOR 2, of which form part of an asymmetrical clock oscillator (24). A four stage Smitt Trigger circuit (25) functions as a de-bouncing circuit to avoid false operation by contacts (17), while a dual flip-flop integrated circuit is connected with section FFA arranged to operate in the direct mode and section FFB arranged as a clocked type D flip-flop. A detonator is fired by current passing through a triggered SCR to disseminate dye from the marking device (20) (FIG. 2). If the key is turned in the time lock (10) to cause its contacts (18) to close, or if the door (5) is opened to effect closure of contacts (23), the input D of section FFB goes high and this is held by the time constant of capacitor C1 and resistor R1 long enough for a clock pulse from oscillator (24) to clock section FFB and send output Q high which will trigger the SCR and cause the detonator to explode. 
     However, if the key in key switch (9) is turned section FFA of the flip-flop is set at its input to send output Q high which will cause transistor TR1 to conduct and effectively by-pass oscillator (24) pulses from the CLK input to flip-flop section FFB. Thus, if key switch (9) is operated in advance of contacts (18) or (23) closing, no clock input will be applied to section FFB and the detonator will not be activated. Output Q goes low with setting of unit FFA which will derive a high at the output of gate NOR 4. The output current of the gate is applied to the LED (13) via current amplifier transistor TR3. LED (13) will flash due to pulsing from the clock oscillator (24). 
     When the timer lock switch (10) has completed a first time period as described hereinbefore, contact (17) will close to disconnect battery from the input of the Smitt Trigger (25) so that the output thereof goes low and through gate NOR 3 current is passed via amplifier TR2 to cause LED 14 to flash. With both LED 13 and LED 14 in a flashing mode the operator is alerted to the fact that the security system is in a permissive state for opening of the door 5. This function can then be performed by again turning the key in the time lock (10). Although the first and second time periods of the time lock (10) are selectively predetermined, in one form the first period may include an interval of 20 minutes while the second permissible period may comprise 1 minute. At the conclusion of the second, permissive, period contacts (17) and (18) will open and the interlock circuitry will become reset. Resetting occurs due to the output of the Trigger (25) going high which will firstly extinguish LED 14 and secondly reset flip-flop section FFA through capacitors C2 which will cause output Q to go high and extinguish LED 13. Resistor R4 establishes a discharge time constant of capacitor C1 to ensure that contacts (18) and (23) are provided with added time for opening after the circuit has been reset. Capacitor C3 and resistors R3 and R5 are provided at the input of section FFA of flip-flop for similar purposes to that described in respect of section FFB. 
     It will now be appreciated that in order to avoid dye marking of the contents of the safe (4) a predetermined sequence of operations in respect of the security system must be adhered to. It is envisaged that the two keys required for opening of the door (5) will be in the possession of different personnel, for example one key may be retained by a member of the bank staff while the other is possessed by a security guard or even at a location remote from the premises on which the safe (4) is installed. The necessary sequence of operations involves turning of the key in the key switch (9) with subsequent turning of key in the time lock (10), and subsequently while both LED 13 and LED 14 are flashing the key of the time lock may again be turned to effect withdrawal of the locking bolt on the door (5). 
     Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, refinements and modifications are possible within the scope of this invention.