Patent ID: 7663483

Claim:
A security device for detecting that detects movement of a provided portal cover, the security device comprising: a sensor that provides indicia of a magnitude of a magnetic flux through the sensor; a magnet that provides the magnetic flux through the sensor; and a processor that receives the indicia of the magnitude of the magnetic flux and detects a change in the magnitude of the magnetic flux outside an upper boundary and a lower boundary of a first threshold and an upper boundary and a lower boundary of a second threshold; wherein: the sensor does not move with respect to the magnet; movement of the sensor and with respect to at least one of the portal cover and a portal changes the magnitude of the magnetic flux through the sensor; the processor determines an average value of a series of values of the indicia of the magnitude of the magnetic flux that fall within the upper boundary and the lower boundary of the first threshold; and the upper boundary and the lower boundary of the first threshold and the second threshold respectively are set in accordance with the average value.