Abstract: An article surveillance security system with self-alarm operates at 6 through 10 MHz as a central frequency, receives a swept low level radio wave within ±5 through 15% from the central frequency, and sounds the alarm. It includes a tuning circuit (1) tuning to the central frequency, and a differential amplifier (2) for amplifying and detecting the output of the tuning circuit. The load resistance (R1) of the differential amplifier is set to 3 through 5 M&OHgr;, and the operating current of the differential amplifier is set to 3 &mgr;A or less. The base-emitter of the amplification/detection transistor (Tr1) of the differential amplifier are connected to the base-emitter of another diode-connected transistor (Tr2) to stabilize a bias drift by temperature. Thus, a receiving circuit of an article surveillance security system with self-alarm (tag) is realized with ability having a power supply of approximately four-year durability, stably operating with a very low level radio wave at 8.

Abstract: An identification code input board for activating electrical equipment such as an electrical lock includes: a display panel crosswise arranged in the form of M lines X N rows while including a plurality of display sections to display a group of codes of which number is represented by a numeral of m X n, a transparent key switch sheet superimposed on the front surface of the display panel while including a plurality of switches arranged corresponding to the display sections, a display converter for selecting one of plural kinds of display formats, of which number is represented by a numeral of (M-m+1) X (N-n+1), every time the electrical equipment is actuated, and a code reader adapted to output a digitized code signal for distinguishing a selected code, wherein each of m and n is a positive integral number of two or more and each of M X N is a positive integral number larger than that of m and n respectively.