Security systems

Claim 2

A security system including at least one portable token embodying a generator and transmitter of oscillations at a predetermined frequency, a pickup at a certain location and means in the pickup for responding to the oscillations transmitted from the token when the token is carried in any atatitude by A user who comes to the location, a sensor responsive to arrival of a person at the location, and a control unit rendered operative by response of the sensor and having means for providing a local reference signal, means responsive to the pick-up response and the local reference signal for forming an output signal, and means receiving the output signal for detecting whether the pickup is responding to oscillations at the predetermined frequency, and to deliver a control signal to dependence upon such detection.

Claim 3

A system as claimed in claim 1 in which the pickup comprises two inductive loops and the control unit includes phase shifters for shifting the phase of signals picked up by the different loops by different phase angles, and means for combining the phase-shifted signals.

Claim 4

A system as claimed in claim 1 in which the token is capable of simultaneously transmitting oscillations at two different predetermined frequencies and including means in the control unit for detecting whether oscillations at both the predetermined frequencies are being picked up by the pickup.

Claim 5

A system as claimed in claim 1 including a plurality of tokens at least one of which is capable of transmitting oscillations at at least one predetermined frequency and at least one other of which is capable of transmitting oscillations at at least one different frequency, and means in the control unit for detecting whether the one predetermined frequency is present at one location and whether the different frequency is present at another location.

Claim 6

A security system as claimed in claim 4 in which the control unit is arranged to deliver a control signal whether the one or the other frequency is present to be picked up at one of the locations.

Claim 7

A system as claimed in claim 1 in which the or each token is arranged to transmit continuously without requiring any action by the person carrying it.

Claim 8

A security system as claimed in claim 1 additionally comprising a socket for each token and a battery charger for automatically charging batteries in the tokens when they are inserted in their sockets.

Claim 9

A system as claimed in claim 1 in which the control unit includes a local oscillator oscillating at a frequency displaced from the predetermined frequency for producing beat frequency pulses and a detector circuit for distinguishing between beat frequencies above and below a certain limit.

Claim 10

A system as claimed in claim 8 in which the beat frequency pulses are passed through a low pass filter in the control unit for cutting off beat frequencies outside a permitted range.

Claim 11

A system as claimed in claim 9 including in the control unit a counter gate for counting beat frequency pulses over a predetermined time interval and means for detecting whether the count achieved is greater or less than a predetermined count.

Claim 12

A system as claimed in claim 10 including means for the control unit for detecting whether no pulses are received over an interval and means connected to the counter gate and providing a wave signal for delimiting the inverval.

Claim 13

A system as claimed in claim 10 including a logic circuit arranged to give an accept signal for controlling the deterrent in dependence on the count of the counter.

Claim 14

A system as claimed in claim 12 wherein the logic circuit includes means for initiating a further detection cycle automatically in response to no accept signal being given within a predetermined time.

Claim 15

A system as claimed in claim 13 including means for giving no alarm if, but only if, an acceept signal is given after at least two detection cycles.

Claim 16

A system as claimed in claim 8 including in the control unit means for modulating the local oscillator frequency by a few cycles for a fraction of a detecting cycle and not for the remainder of the cycle, means providing a wave signal for delimiting the detecting cycle and means responsive to the wave signal for delimiting fractions of the cycle.

Claim 17

A system as claimed in claim 15 including in the control unit gates for counting beat frequency pulses in one sense for the fraction of the cycle and in the other sense for the remainder of the cycle.

Claim 18

A security system as claimed in claim 1 including a deterrent and means responsive to the control signal for operating the deterrent.

Claim 19

A system as claimed in claim 17 in which the deterrent comprises a door having a lock arranged to be operated in response to the control signal from the control unit.

Claim 20

A system as claimed in claim 17 in which the deterrent comprises an alarm arranged to be operated in response to the control signal from the control unit.

Claim 21

A security system as claimed in claim 1 including an exit loop detector at an exit from premises and in which the control unit responds to a signal from the exit loop detector due to a token being taken through the exit.

Claim 22

A security system for operating a deterrent comprising: a portable token for carrying within the system, the token having means for generating and transmitting oscillations at two different frequencies; a loop system at a certain location in the system for providing an output signal including the oscillation frequencies from the token, the loop system having two inductive loops in substantially perpendicular planes for picking up the oscillations from the token when the token is carried in any attitude near the location of the loop system and means combining the signals from the loops for providing the output signal; and a control unit receiving the output signal from the loop system for transmitting a signal operating the deterrent, the control unit having a detecting system, the detecting system having two detecting circuits each receiving the output signal from the loop system and each having a local oscillator arranged to oscillate at a frequency displaced from that of a different one of the token oscillation frequencies in the loop system output signal, means mixing the loop system output signal with the local oscillator frequency for forming beat frequency pulses, and a gate arranged to count the beat frequency pulses during at least part of a signal from a clock for passing a signal having a 0 or 1 state dependent upon the counting of a predetermined number of beat pulses during the clock signal, the control unit also having a clock for providing the clock signal to each gate and means responsive to the state of the signal from each gate for providing the signal operating the deterrent.

Claim 23

A security system for operating a deterrent comprising: a portable token for carrying within the system, the token having means for generating and transmitting oscillations at two different frequencies; a loop system at a certain location in the system for providing an output signal including the oscillation frequencies from the token, the loop system having two inductive loops in substantially perpendicular planes for picking up the oscillations from the token when the token is carried in any attitude near the location of the loop system and means combining the signals from the loops for providing the output signal; and a control unit receiving the output signal from the loop system for transmitting a signal operating the deterrent, the control unit having a detecting system, the detecting system having two detecting circuits each receiving the output signal from the loop system and each having a local oscillator arranged to oscillate at a frequency displaced from that of a different one of the token oscillation frequencies in the loop system output signal, means mixing the loop system output signal with the local oscillator frequency for forming beat frequency pulses, and a gate arranged to count the beat frequency pulses during at least part of a signal from a clock for passing a signal having a 0 or 1 state dependent upon the counting of a predetermined number of beat pulses during the clock signal, the control unit also having a clock for providing the clock signal to each gate and means responsive to the state of the signal from each gate for providing the signal operating the deterrent.

Claim 24

A system as in claim 21 wherein the means combining the signals from the loops in the loop system comprise means for oppositely shifting the phase of the signal picked up by each loop and means adding each of the oppositely phase-shifted signals for providing the output signals.