Adjustable security sensing device

A multiple-frame Fresnel lens sheet comprising:

• a first row of a plurality of Fresnel lenses with a first focal length;
• a second row of a plurality of other Fresnel lenses with a second focal length;
• wherein said first focal length and said second focal length are different;
• wherein each member of said first row of a plurality of Fresnel lenses has a first diameter measured on a principle plane of said each member of said first row of a plurality of Fresnel lenses;
• wherein each member of said second row of a plurality of other Fresnel lenses has a second diameter measured on said principle plane of said each member of said second row of a plurality of other Fresnel lenses;
• wherein said first diameter is different from said second diameter;
• wherein said first focal length is longer than said second focal length;
• and
• wherein said first diameter is smaller than said second diameter.

A method of creating an adjustable sensing device, comprising:

• providing an electromagnetic sensor, having a surface with a plurality of different electromagnetic radiation interception areas arranged one above the other;
• mounting a lens in front of said electromagnetic sensor;
• mounting a controllable flap in front of said electromagnetic sensor, either in front of said lens or between said lens and said electromagnetic sensor;
• and
• mechanically attaching a control mechanism to one side of said controllable flap such that changing the position of said controllable flap changes the part of said electromagnetic sensor covered by said controllable flap.