A protective alarm system for a vehicle or the like wherein a protective switch initiates operation of a circuit combining two timing effects : effecting time delaying of an alarm device, and determining the duration of the alarm. Once initiated by the protective switch, the alarm is actuated after a predetermined delay and for a predetermined duration despite any action on the switch such as a periodical opening and closing. Circuitry operated by a key switch defeats instantaneously actuation of the alarm system when a further manually operated knob is on, which results in a necessary order of operation, involving the possession of the key, to inhibit definitely the alarm.
A motor vehicle antitheft alarm provides complex sounds, is disabled in normal use of the vehicle, and is resistant to "hotwiring" of the ignition notwithstanding. Unauthorized motion of the vehicle causes a disturbance sensor to activate the alarm circuit. Qualitatively different alarm sounds are provided in response to repeated disturbances as compared with isolated ones. When the ignition is turned on in normal use, a first voltage condition is provided to disable the alarm apparatus. After the ignition is turned off a short time of disabling is provided to permit the user to leave the vehicle before the alarm can be activated. An anti-hotwiring turn-on circuit associated with the ignition switch provides a second voltage condition, or allows same, blocking the first voltage condition from occurring during hotwiring. A voltage-sensitive circuit sets off the alarm when the second voltage condition occurs, deterring hotwiring. The alarm automatically turns off after a period of time, conserving battery power and affording owner convenience. When the vehicle is a motorcycle or moped, the center stand is provided with a switch for preventing alarm sounds during normal maintenance with the center stand down. A backup battery and other circuit-protecting measures are providable in the alarm unit which is located in a secure part of the vehicle.
