Abstract: An anti-theft system which is armed only when a hand-held coded transmitter is operated; the system is disarmed upon a subsequent operation of the transmitter. Whenever the transmitter is operated, the horn beeps, and the lights flash; this provides both verification that the system is armed, and serves as a car-locating aid in a parking field. Tampering with the automobile results in intermittent beeping of the horn and flashing of the lights. The horn beeping may be disabled during the verification and car locating sequences, while still operating if unauthorized access to the automobile is attempted. Other features include disabling of the horn beeping by momentarily turning on the ignition; beeping of the horn after the system is disarmed and a door is opened by the operator if, during his absence, unauthorized access was attempted; locking and unlocking of the doors with transmitter operation; and detection of unauthorized access attempts by sensing vibrations in the vehicle radio loudspeakers.

Abstract: There is disclosed a miniature hand-held radio-frequency transmitter. An operating frequency is determined by a lumped-circuit oscillator which feeds an antenna etched on the periphery of the circuit board. The antenna is tuned to a frequency which is slightly above the second harmonic of the operating frequency, it being the second harmonic which is radiated. By slightly mis-tuning the antenna, the effects of an enveloping hand are minimized. The clasping of the transmitter by a human hand results in the absorption of some of the radiated power, but hand-capacitance effects also shift the center frequency of the antenna characteristic toward the second harmonic of the operating frequency, thus increasing the radiated power. In this way the signaling range under free-space conditions is the same as that under operating conditions. The oscillator circuit can thus be adjusted for maximum power output under free-space conditions within the guidelines of F.C.C.