Vehicle back-up alarm

A backup alarm for vehicles for producing a pulsed audio signal, comprising:

• sound generator means having an input and an output, said generator comprising an audio frequency oscillator producing audio frequency signals at its output;
• means providing a variable time constant for for said audio frequency oscillator to vary the tone of said audio frequency signals;
• blocking pulse generating means having an input and an output, said blocking pulse generating means comprising a sub-audio frequency oscillator producing periodic blocking pulses at its output;
• amplifier means having an input and an output;
• means connecting the output of said sound generator means to said amplifier input to apply said audio frequency signals to said amplifier means;
• means connecting the outputs of said blocking pulse generating means and said sound generator means in parallel to said amplifier input and for connecting the output of said blocking pulse generator through a feedback loop to the input of said sound generator means, whereby the presence of a blocking pulse at the output of said blocking pulse generating means disables and amplifying means and said sound generator means;
• sound producing means;
• means connecting said amplifier output to said sound producing means, whereby said audio frequency output signals are amplified and applied to said sound producing means in the absence of said blocking pulses;
• and
• voltage limiter means comprising negative feedback means connected between the output and the input of said amplifier means to regulate the voltage provided at said amplifier output so that said alarm is adaptable for use with a variety of vehicles, and is operable with various power supply voltages.