Abstract: A security and alarm apparatus has a pulse width discriminator circuit which includes: a monostable multivibrator having a trigger input connected to a data input of a flip-flop, a data output connected to a clock input of the flip-flop, and a pulse width control input; and a pulse width control circuit connected to the pulse width control input which causes a pulse produced by the monostable multivibrator to have one width when the flip-flop is in a first state and a larger width when the flip-flop is in a second state, the flip-flop producing at its data output a signal which is a logic high voltage when the frequency of an input signal at the trigger input has exceeded a first predetermined frequency and until it thereafter falls below a second predetermined frequency less than said first predetermined frequency, and which is a logic low voltage when the input signal has fallen below the second predetermined frequency until the input signal again exceeds the first predetermined frequency.

Abstract: A method and apparatus are provided for transmitting from a radio transmitter which is part of a first system to a radio receiver which is part of a second system a message which includes a plurality of characters arranged in a predetermined sequence. Each character of the message is transmitted in the form of a 48-bit binary word, the first byte of the word being a start byte, the second and third bytes being identical binary numbers representing the position in the message of a selected one of the characters, the fourth and fifth bytes being identical binary numbers which are the ASCII code corresponding to the selected character, and the sixth byte being a stop byte which is a predetermined binary number different from the start byte.