Single-element door/window opening detector

An article proximity detection method, comprising:

• receiving a first indication of a measurement of a resonant frequency of an antenna, said antenna having at least a first resonant frequency and a second resonant frequency associated therewith, said second resonant frequency being different from said first resonant frequency, said antenna having said first resonant frequency when in proximity to an article having a given dielectric constant and having said second resonant frequency when not in proximity to said article having said given dielectric constant;
• generating a direct electrical current corresponding to an intensity of a reflected electromagnetic signal received from said antenna;
• converting said direct electrical current into a digital value corresponding to said intensity of said reflected electromagnetic signal;
• ascertaining, based on said digital value corresponding to said intensity of said reflected electromagnetic signal, whether said resonant frequency of said antenna has changed from said first resonant frequency to said second first resonant frequency;
• and
• in response to ascertaining that said resonant frequency of said antenna has changed from said first resonant frequency to said second resonant frequency, for generating a second indication indicating that said antenna is not in proximity to said article.

A door\window opening detector, comprising:

• an antenna having at least a first resonant frequency and a second resonant frequency associated therewith, said second resonant frequency being different from said first resonant frequency, said antenna having said first resonant frequency when in proximity to a door\window having a given dielectric constant and having said second resonant frequency when not in proximity to a door\window having said given dielectric constant;
• a high-frequency detector operable for generating a direct electrical current corresponding to an intensity of a reflected electromagnetic signal received from said antenna;
• an analog to digital converter communicating with said high-frequency detector and operable for receiving said direct electrical current corresponding to said intensity of said reflected electromagnetic signal from said high-frequency detector and for converting said direct electrical current into a digital value corresponding to said intensity of said reflected electromagnetic signal;
• and
• an alarm indication generator operable:
• for receiving said digital value from said analog to digital converter;
• and
• for ascertaining, based on said digital value corresponding to said intensity of said reflected electromagnetic signal, whether a resonant frequency of said antenna has changed from said first resonant frequency to said second first resonant frequency;
• and
• in response to ascertaining that said resonant frequency of said antenna has changed from said first resonant frequency to said second resonant frequency, for generating an alarm indication of opening of said door\window.

A door\window opening detection method, comprising:

• receiving an indication of a measurement of a resonant frequency of an antenna, said antenna having at least a first resonant frequency and a second resonant frequency associated therewith, said second resonant frequency being different from said first resonant frequency, said antenna having said first resonant frequency when in proximity to a door\window having a given dielectric constant and having said second resonant frequency when not in proximity to said door\window having said given dielectric constant;
• generating a direct electrical current corresponding to an intensity of a reflected electromagnetic signal received from said antenna;
• converting said direct electrical current into a digital value corresponding to said intensity of said reflected electromagnetic signal;
• ascertaining, based on said digital value corresponding to said intensity of said reflected electromagnetic signal, whether said resonant frequency of said antenna has changed from said first resonant frequency to said second first resonant frequency;
• and
• in response to ascertaining that said resonant frequency of said antenna has changed from said first resonant frequency to said second resonant frequency, generating an alarm indication of an opening of said door\window.