Appliance theft prevention alarm system

Claim 1

A theft prevention alarm system for use with an electrical appliance comprising: a transmitter including a power plug for connection within the case of an electrical appliance to the alternating current power cord of the electrical appliance, said transmitter including an oscillator operable by electrical power supplied through the power cord of the appliance to generate an electrical signal of a predetermined frequency, a transformer connected between said oscillator and the power cord to couple said electrical signal into the alternating current power supply, a receiver including an isolation transformer for connection into the alternating current power supply remote from said appliance, a rectifier connected to said isolation transformer for providing DC bias voltage for said receiver, a tuned circuit tuned to said predetermined frequency, a second transformer for coupling said electrical signal having the predetermined frequency to said tuned circuit, amplifier means for amplifying the output from said tuned circuit, switch means operable by the output from said tuned circuit, and an alarm system operable in response to said switch means to provide an alarm indication when said receiver ceases to detect said predetermined frequency electrical signal.