Editing Security alarm (section)

==== Digital analysis of the signal ====
The more recent and higher performance models of these detectors generate a detection whether the intruder is rolling, crossing, crawling or moving very slow within the [[electromagnetic field]]<ref>{{Cite book |last1=De Astis |first1=Vincenzo |title=Security technology handbook |last2=Gasparini |first2=Bruno |publisher=Assosicurezza |year=2002 |location=Milano |pages=100–102 |language=en}}</ref> reducing false alarms. The [[ellipsoid]]al shape of the longitudinal section however does not allow a good detection capability close to the receiver or transmitter heads, and those areas are commonly referred to as "dead zones". A solution to avoid this problem, when installing 2 or more barriers, is to cross the respective transmitter and receiver heads some meters from the respective heads or to use mono-head sensor to cover the dead zones.<ref>{{Cite journal |date=2012 |title=Guide to Perimeter Intrusion Detection Systems (PIDS) |url=https://www.cpni.gov.uk/resources/perimeter-intrusion-detection-systems-guidance-document |journal=CPNI - Centre for the Protection of National Infrastructure |number=5/12 |pages=24–38}}</ref>