False alarm avoidance system

1. A method carried out in a tag for a localisation system, the method comprising at said tag:

operating a magnetic induction signal detection circuit to detect signals emitted by one or more beacons;

upon detection by said magnetic induction signal detection circuit of a magnetic induction signal comprising a first identification code:

correlating the magnetic induction signal comprising said first identification code to an ultrasound signal emitted by said one or more beacons, said ultrasound signal being suitable for obtaining room-level localisation accuracy and comprising a second identification code, received by said tag via an ultrasound signal detection circuit; and

if said correlation reveals an association between said first identification code and said second identification code: transmitting a radio frequency announcement signal via a radio frequency signal transmitter circuit to signify said association.

2. The method according to claim 1 , wherein said ultrasound signal detection circuit is activated at said tag upon detection of the magnetic induction signal.

3. The method according to claim 2 , wherein said tag transmits a radio frequency request signal comprising said first identification code upon detection of the magnetic induction signal to trigger transmission of said ultrasound signal by said one or more beacons.

4. The method according to claim 3 , wherein said radio frequency request signal comprises tag identification information.

5. The method according to claim 1 , wherein said ultrasound signal detection circuit is operated prior to said detection, and wherein said second identification code is stored in a memory at said tag upon receipt of said ultrasound signal, and wherein said correlating comprises correlating said first identification code from said magnetic induction signal to said stored second identification code.

6. The method according to claim 1 , wherein said radio frequency announcement signal comprises tag identification information.

7. A method carried out in a beacon for a localisation system, the method comprising, at said beacon:

operating a magnetic induction signal transmission circuit to transmit a magnetic induction signal comprising a first identification code;

operating a radio frequency signal detection circuit;

upon detection by said radio frequency signal detection circuit of a radio frequency announcement signal:

evaluating whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: asserting a localisation alert.

8. The method according to claim 7 , wherein said beacon further comprises said ultrasound signal transmission circuit, and further comprising transmitting said ultrasound signal via said ultrasound signal transmission circuit.

9. The method according to claim 8 , wherein said ultrasound signal transmission circuit is activated upon detecting a radio frequency request signal comprising said first identification code.

10. The method according to claim 8 , wherein said ultrasound signal transmission circuit is operated in a continuous mode.

11. A system comprising one or more tags configured to carry out the method according to claim 1 and one or more beacons configured to:

operate a magnetic induction signal transmission circuit to transmit the magnetic induction signal comprising said first identification code;

operate a radio frequency signal detection circuit;

upon detection by said radio frequency signal detection circuit of said radio frequency announcement signal:

evaluate whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: assert a localisation alert.

12. A computer program product comprising code means configured to cause a processor in a tag to perform the steps of the method according to claim 1 .

13. A computer program product comprising code means configured to cause a processor in a beacon to perform the steps of the method according to claim 7 .

14. The method according to claim 2 , wherein said radio frequency announcement signal comprises tag identification information.

15. The method according to claim 5 , wherein said radio frequency announcement signal comprises tag identification information.

16. The method according to claim 6 , wherein said radio frequency announcement signal comprises tag identification information.

17. A system comprising:

one or more tags configured to carry out the method according to claim 2 ; and

at least one beacon configured to:

operate a magnetic induction signal transmission circuit to transmit the magnetic induction signal comprising said first identification code;

operate a radio frequency signal detection circuit; and

upon detection by said radio frequency signal detection circuit of said radio frequency announcement signal:

evaluate whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: assert a localisation alert.

18. A system comprising:

one or more tags configured to carry out the method according to claim 5 ; and

at least one beacon configured to:

operate a magnetic induction signal transmission circuit to transmit the magnetic induction signal comprising said first identification code;

operate a radio frequency signal detection circuit; and

upon detection by said radio frequency signal detection circuit of said radio frequency announcement signal:

evaluate whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: assert a localisation alert.

19. A system comprising:

one or more tags configured to carry out the method according to claim 6 ; and

at least one beacon configured to:

operate a magnetic induction signal transmission circuit to transmit the magnetic induction signal comprising said first identification code;

operate a radio frequency signal detection circuit; and

upon detection by said radio frequency signal detection circuit of said radio frequency announcement signal:

evaluate whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: assert a localisation alert.

20. A system comprising:

one or more tags configured to carry out the method according to claim 1 ; and

at least one beacon comprising an ultrasound signal transmission circuit, wherein the at least one beacon is configured to:

operate a magnetic induction signal transmission circuit to transmit the magnetic induction signal comprising said first identification code;

operate a radio frequency signal detection circuit;

transmit said ultrasound signal via said ultrasound signal transmission circuit; and

upon detection by said radio frequency signal detection circuit of said radio frequency announcement signal:

evaluate whether said radio frequency announcement signal signifies an association between said first identification code and a second identification code of an ultrasound signal emitted by said beacon or a different beacon in the same room by use of an ultrasound signal transmission circuit, comprising said second identification code, and,

conditionally upon evaluating said association: assert a localisation alert.