Personnel monitoring tag with tamper detection and secure reset

• US 5,075,670 A
• Filed: 08/01/1990
• Issued: 12/24/1991
• Est. Priority Date: 08/01/1990
• Status: Expired due to Term

• Current Assignee: Digital Products Corp.
• Original Assignee: Digital Products Corp.
• Inventors: Bower, David S., Davies, Ronald C.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US07/561,443
• Time in Patent Office: 510 Days
• Field of Search: 340/573, 340/539, 340/572
• US Class Current: 340/573.4
• CPC Class Codes: G08B 21/22 responsive to presence or absence of persons
• CPC Class Codes: G08B 29/046 prevention of tampering with detection circuits

Abstract

A signalling tag of the type used in house arrest systems has a tamper detection device for detecting removal of the tag from the monitored person. The signal is set to a tamper condition upon removal. The tamper detector can only be reset to the normal state by a reset signal which incorporates a characteristic of the signal sent by the tag. This provides enhanced protection against attempts by the monitored person to defeat the system through unauthorized resetting.

Claims

1. A personnel monitoring tag comprising:

(a) tamper latch means having a normal state and a tamper state;

(b) tag signal means including means for sending a tamper tag signal having a predetermined characteristic when said tamper latch means is in said tamper state;

(c) securement means for securing said tag to a person to be monitored;

(d) tamper detect means for detecting detachment of said tag from said person to be monitored and pacing said tamper latch means in said tamper state in response to such detachment; and

(e) reset means for resetting said tamper latch means to said normal state only in response to a reset signal replicating said predetermined characteristic of said tamper tag signal, whereby said reset means can be actuated only by receiving said tag signal so as to determine said predetermined characteristic thereof and producing a reset signal replicating such predetermined characteristic.

2. A tag as claimed in claim 1 wherein said tag signal means includes means for sending said tamper tag signal only during discrete transmission intervals, and wherein said reset means includes means for resetting said tamper latch means only in response to a reset signal bearing a predetermined time relationship with said transmission intervals of said tag signal.

3. A tag as claimed in claim 2 wherein said reset means includes means for resetting said tamper latch means only in response to a reset signal which commences during one of said transmission intervals of said tamper tag signal.

4. A tag as claimed in claim 3 wherein said tag signal means includes potential source means for providing a first potential during said transmission intervals and providing a second potential different from said first potential except during said intervals, a transmitter connected to said potential source means and operative to transmit said tamper tag signal in response to said first potential when said tamper latch means is in said tamper state, and wherein said reset means includes signal storage means for storing a first signal responsive to said first potential and a second signal responsive to said second potential, said reset means further including switch means for connecting said signal storage means to said potential source means except during application of said reset signal and disconnecting said signal storage means from said potential source means and connecting said signal storage means to said tamper latch means during application of said reset signal, said tamper latch means being settable to said normal state upon application of said first signal to said tamper latch means by said signal storage means, whereby said signal storage means will store said second signal except during said transmission intervals and will store said first signal only during said intervals, and said signal storage means will apply said first signal to said tamper latch means only if said reset signal commences during one of said transmission intervals.

5. A tag as claimed in claim 4 wherein said signal storage means includes a capacitor.

6. A tag as claimed in claim 4 wherein said switch means includes a magnetically actuatable switch.

7. In combination, a tag as claimed in claim 6 and a resetting tool including means for receiving said tamper tag signal and means for generating a magnetic field only while said tamper tag signal is being received.

8. In combination, a tag as claimed in claim 1 and a resetting tool including means for receiving said tamper tag signal, means for determining said predetermined characteristic of said tamper tag signal and means for generating said reset signal so that said reset signal matches said predetermined characteristic of said tamper tag signal and applying said reset signal to said tag.

9. A resetting tool for a personnel monitoring tag comprising means for receiving a tag signal from said personnel monitoring tag, means for determining a predetermined characteristic of said tag signal and means for generating a reset signal so that said reset signal matches a predetermined characteristic of said tag signal and applying said reset signal to the tag.

10. A tool as claimed in claim 9 wherein said means for determining a characteristic includes means for determining when said tag signal is being received and said means for generating a reset signal includes means for generating said reset signal in a predetermined time relationship to reception of said tag signal.

11. A tool as claimed in claim 10 wherein said means for generating said reset signal includes means for generating said reset signal only while said tag signal is being received.

13. A tool as claimed in claim 10 wherein said means for generating said tag signal includes means for generating a magnetic field and applying said magnetic field to the personnel monitoring tag.

12. A tool as claimed in claim wherein said means for generating said reset signal includes means for delaying commencement of said reset signal until a predetermined delay time has elapsed after reception of said tag signal has commenced.

14. A personnel monitoring tag comprising:

(a) tag signal means for sending a tag signal;

(b) reference means for providing a source of a reference potential;

(c) tamper latch means having a normal state and a tamper state, said tag signal means including means for sending a normal tag signal when said tamper latch means is in said normal state and a tamper tag signal when said tamper latch means is in said tamper state, said tamper latch means having a trip input and being responsive to change from said normal state to said tamper state upon application to said trip input of a trip potential different from said reference potential;

(d) securement means for securing said tag signal means to a person to be monitored;

(e) connection means for electrically connecting said trip input to said reference potential through said securement means so that said connection will be broken if said securement means is disrupted;

(f) alternating potential source means for providing a potential alternating between first and second potentials, at least one of said first and second potentials being different from said reference potential; and

(g) a capacitor, said trip input of said tamper latch being connected to said alternating potential source means through said capacitor, whereby, if said connection through said securement means is broken, said alternating potential applied by said alternating potential source means will be applied to said trip input and said tamper latch will be set to said tamper state.

15. A tag as claimed in claim 14 wherein said connection means includes a first resistor connected between said trip input and said reference potential, said capacitor being connected to said trip input through said first resistor.

16. A tag as claimed in claim 15 further comprising DC source means for providing a substantially constant potential different from said reference potential and a second resistor having a resistance higher than said first resistor connected between said DC source means and said trip input.

17. A tag as claimed in claim 16 further comprising alternate path means for connecting said trip input to said DC source means through a path having an impedance lower than the resistance of said second resistor upon attempted disruption of said securement means.

18. A tag as claimed in claim 14 wherein said tag signal means includes a radio transmitter connected to said alternating potential source and responsive to one of said first and second potentials to send said tag signal, whereby said transmitter will send said tag signal intermittently.

19. A tag as claimed in claim 18 wherein said alternating potential source means is operative to apply said first potential only during predetermined intervals so that there are dwell periods between said intervals, said dwell periods being substantially longer than said intervals, said transmitter being responsive to said first potential to send said tag signal.