Methods and apparatus for security device removal detection

1. A security device that detects removal of the device from a provided surface, the security device comprising:

a body;

at least one magnet coupled to the body; and

a sensor coupled to the body proximate to at least one of the at least one magnet; wherein:

the sensor does not move with respect to the at least one magnet;

the at least one magnet provides a magnetic flux;

magnetically coupling the at least one magnet to the surface conducts at least a portion of the magnetic flux away from the sensor; and

decoupling the at least one magnet from the surface conducts at least a portion of the magnetic flux through the sensor thereby indicating removal of the body from the surface.

2. The security device of claim 1 wherein:

the body comprises a metal plate; and

at least two magnets magnetically couple to the plate.

3. The security device of claim 1 wherein:

the sensor comprises a sensing axis; and

the sensing axis is oriented perpendicular to an axis between a south pole and a north pole of at least one of the at least one magnet.

4. The security device of claim 1 wherein:

the at least one magnet comprises a u-shaped magnet; and

the sensor is positioned in a cavity of the u-shaped magnet between a north pole and a south pole.

5. The security device of claim 1 wherein:

the at least one magnet comprises a magnet having a cavity; and

the sensor is positioned in the cavity.

6. The security device of claim 1 wherein:

the at least one magnet comprises a first magnet and a second magnet; and

the sensor is positioned between the first magnet and the second magnet.

7. The security device of claim 6 wherein:

the first magnet and the second magnet each have a north pole and a south pole;

the north pole of the first magnet couples to the body; and

the south pole of the second magnet couples to the body.

8. The security device of claim 7 wherein decoupling at least one of the first magnet and the second magnet from the surface conducts at least a portion of a magnetic flux between the south pole of the first magnet and the north pole of the second magnet through the sensor.

9. The security device of claim 7 wherein coupling at least one of the first magnet and the second magnet to the surface conducts at least a portion of the magnetic flux between the south pole of the first magnet and the north pole of the second magnet away from the sensor through the surface.

10. The security device of claim 1 wherein the sensor comprises a Hall effect sensor.

11. The security device of claim 1 wherein the sensor provides a signal when the flux conducted through the sensor is great than a threshold.

12. A removal detector that detects the removal of a provided security device from a provided surface, the detector comprising:

at least one magnet; and

a sensor positioned proximate to at least one of the at least one magnet; wherein:

the at least one magnet couples to the security device;

the sensor couples to the security device;

the sensor does not move with respect to the at least one magnet;

the at least one magnet provides a magnetic flux;

magnetically coupling the at least one magnet to the surface conducts at least a portion of the magnetic flux away from the sensor; and

decoupling the at least one magnet from the surface conducts at least a portion of the magnetic flux through the sensor thereby indicating removal of the security device from the surface.

13. The removal detector of claim 12 wherein:

the sensor comprises a sensing axis; and

the sensing axis is oriented perpendicular to an axis between a south pole and a north pole of at least one of the at least one magnet.

14. The removal detector of claim 12 wherein:

the at least one magnet comprises a u-shaped magnet; and

the sensor is positioned in the u-shaped magnet between a north pole and a south pole.

15. The removal detector of claim 12 wherein:

the at least one magnet comprises a magnet having a cavity; and

the sensor is positioned in the cavity.

16. The removal detector of claim 12 wherein:

the at least one magnet comprises a first magnet and a second magnet; and

the sensor is positioned between the first magnet and the second magnet.

17. The removal detector of claim 16 wherein:

the first magnet and the second magnet each having a north pole and a south pole;

the north pole of the first magnet couples to the security device; and

the south pole of the second magnet couples to the security device.

18. The removal detector of claim 17 wherein decoupling at least one of the first magnet and the second magnet from the surface conducts at least a portion of a magnetic flux between the south pole of the first magnet and the north pole of the second magnet through the sensor.

19. The removal detector of claim 17 wherein magnetically coupling at least one of the first magnet and the second magnet to the surface conducts a portion of the magnetic flux between the south pole of the first magnet and the north pole of the second magnet away from the sensor through the surface.

20. The removal detector of claim 12 wherein the sensor comprises a Hall effect sensor.

21. The removal detector of claim 12 wherein the sensor provides a signal when the flux conducted through the sensor is great than a threshold.

22. A security device that detects removal of the device from at least one of a first portal cover and a second portal cover, the security device comprising:

a body;

a first removal detector; and

a second removal detector; wherein:

the first removal detector magnetically couples the body to the first cover;

the second removal detector magnetically couples the body to the second cover;

the first removal detector detects removal of the body from the first cover;

the second removal detector detects removal of the body from the second cover;

at least one of the first removal detector and the second removal detector includes:

at least one magnet; and

a sensor positioned proximate to at least one of the at least one magnet; wherein:

the sensor does not move with respect to the at least one magnet;

each one magnet provides a magnetic flux;

magnetically coupling the at least one magnet to at least one of the first portal cover and the second portal cover conducts at least a portion of the magnetic flux away from the sensor; and

decoupling the at least one magnet from at least one of the first portal cover and the second portal cover conducts at least a portion of the magnetic flux through the sensor thereby indicating removal of the security device.

23. A method performed by a security device for detecting removal of the security device from a surface, the device having a body, the method comprising:

detecting a change in a magnitude of a magnetic flux through a sensor; and

providing a signal in accordance with detecting; wherein:

at least one magnet couples to the body of the security device;

the sensor couples to the body proximate to at least one magnet of the at least one magnet;

the sensor does not move with respect to the at least one magnet;

each at least one magnet provides a magnetic flux;

magnetically coupling the at least one magnet to the surface conducts at least a portion of the magnetic flux away from the sensor; and

decoupling the at least one magnet from the surface conducts at least a portion of the magnetic flux through the sensor thereby indicating removal of the security device.

24. The method of claim 23 wherein detecting comprises:

detecting successive magnitudes of the magnetic flux; and

comparing successive magnitudes.

25. The method of claim 23 wherein detecting comprises applying a hysteresis to the change in the magnitude of the magnetic flux.

26. The method of claim 23 wherein detecting comprises detecting a change greater than a threshold.

27. A removal detector that detects the removal of a provided security device from a provided surface, the detector comprising:

at least one magnet; and

a sensor positioned proximate to at least one of the at least one magnet; wherein:

the at least one magnet couples to the security device;

the sensor couples to the security device;

the sensor and the at least one magnet do not move with respect to each other;

the at least one magnet provides a magnetic flux;

magnetically coupling the at least one magnet to the surface conducts at least a portion of the magnetic flux through the surface away from the sensor; and decoupling the at least one magnet from the surface conducts at least a portion of the magnetic flux through the sensor thereby indicating removal of the security device.