Trailer theft and burglary alarm system

• US 4,737,763 A
• Filed: 04/27/1987
• Issued: 04/12/1988
• Est. Priority Date: 04/27/1987
• Status: Expired due to Term

• Current Assignee: Longhorn SCSF, Ltd.
• Original Assignee: Specific Cruise Systems, Inc.
• Inventors: Shields, Neal G., DeFino, John M.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US07/042,731
• Time in Patent Office: 351 Days
• Field of Search: 340/63, 340/635, 340/641, 340/642, 340/686, 340/687, 340/52 R, 307/10 R, 307/10 AT, 307/10 LS
• US Class Current: 340/426.1
• CPC Class Codes: B60R 2325/304 Boats
• CPC Class Codes: B60R 25/1001 Alarm systems associated with another car fitting or mechanism, e.g. door lock or knob, pedals features related to the general power supply B60R25/1018
• CPC Class Codes: B60R 25/1004 Alarm systems characterised by the type of sensor, e.g. current sensing means using door lock sensors B60R25/1001

Abstract

A trailer theft and burglary alarm system utilizes the releasable electrical connection between a vehicle light circuit and the trailer brake light circuit to warn the operator that the releasable electrical connection is being tampered with. A signal producing apparatus continuously monitors the resistance of the trailer brake light circuit and produces a signal corresponding thereto. When the vehicle is to be left unattended, the signal is recorded. Thereafter, if the releasable connection is disconnected, the signal produced will differ from the original signal. This difference is recognized and the alarm sounds. Portal sensors can be provided that will produce a change in either the resistance or capacitance sensed by the signal producing apparatus if a portal to the trailer is disturbed. This change in either resistance or capacitance will also alter the signal produced, and trigger the alarm.

Claims

1. A theft alarm device for the protection of a trailer while connected to a vehicle, the trailer being of the type having an electrical lamp circuit, and plug means for releasably connecting the trailer lamp circuit to a vehicle electrical lamp circuit, comprising:

a signal producing means, located in the vehicle having an input connected to the vehicle lamp circuit, for continuously producing at an output an electrical signal corresponding to the resistance monitored at its input, the resistance at the input including the resistance of the trailer lamp circuit when connected to the vehicle lamp circuit;

an alarm arming means, located in the vehicle, for activating the theft alarm device when the vehicle is left unattended;

means, located in the vehicle, for recording the electrical signal at the time the theft alarm device is activated, and for continuously comparing the signal thereafter produced by the signal producing means with the recorded electrical signal; and

an alarm means, located in the vehicle, for providing a warning signal while the theft alarm device is activated if the electrical signal produced by the signal producing means differs from the recorded electrical signal, indicating that the trailer lamp circuit is being unplugged from the vehicle lamp circuit.

2. The theft alarm device according to claim 1, wherein the signal producing means comprises a variable frequency oscillator, which produces a variable frequency for the electrical signal corresponding to the resistance at the input of the signal producing means.

3. The theft alarm according to claim 2, wherein the oscillator is an astable multivibrator.

4. A theft alarm device for a vehicle for warning of tampering with the releasable electrical connection between a vehicle lamp circuit and the lamp circuit of an electrically connected trailer, comprising in combination:

an oscillator means, located in the vehicle, having an input connected to the vehicle lamp circuit, for monitoring the resistance of the vehicle lamp circuit and generating electrical signals with a frequency corresponding in part to the electrical resistance of the trailer lamp circuit when the trailer lamp circuit is connected to the vehicle lamp circuit;

an alarm arming means, located in the vehicle, for activating the theft alarm device when the vehicle and trailer are to be left unattended;

an alarm means, located in the vehicle, for producing a warning signal;

a processor means, located in the vehicle, for sensing and recording the frequency of the electrical signal produced by the oscillator means at the time of arming, for continuously comparing the recorded frequency with the frequency of the electrical signals thereafter generated by the oscillator means, and for activating the alarm means when a significant difference in frequency is detected; and

a vehicle protection sensor means for detecting intrusion or tampering with the vehicle, and for providing electrical signals to the processor means indicative of intrusion or tampering.

5. The theft alarm device according to claim 4, further comprising:

at least one portal sensor means connected to the trailer lamp circuit, for providing a change in resistance in the trailer lamp circuit if a portal on the trailer is opened, causing the oscillator means to sense a change in resistance and the processor means to activate the alarm.

6. The theft alarm device according to claim 4, further comprising:

at least one portal sensor means connected to the trailer lamp circuit for providing a change in capacitance in the trailer lamp circuit if a portal on the trailer is opened, causing the oscillator means to sense a change in capacitance and the processor means to activate the alarm.

7. A method for protecting a trailer from theft, the trailer being of the type having a lamp circuit electrically connected to a vehicle lamp circuit by a releasable electrical connector, and being hitched to a vehicle having a theft alarm system with an alarm, the method comprising the steps of:

connecting an oscillator means input to the vehicle lamp circuit and generating electrical signals with a frequency corresponding to the electrical resistance monitored at the input, the electric resistance including the trailer lamp circuit resistance;

arming the theft alarm system when leaving the vehicle unattended with the trailer connected;

sensing the frequency of the electrical signals at the moment of arming;

recording the frequency of the electrical signals sensed at the moment of arming;

continuously monitoring the frequency of the electrical signals;

comparing the frequency of the electrical signals with the recorded frequency; and

activating the alarm when the monitored frequency is significantly different from the recorded frequency, indicating that the trailer lamp circuit is being disconnected from the vehicle lamp circuit.