Vehicle alarm

Claim 2

A vehicle alarm system comprising: an alarm; means for coupling a first vehicle accessory to said alarm for triggering said alarm whenever the magnitude of the impedance from said first vehicle accessory to vehicle ground is greater than a first predetermined threshold level; means for coupling a second vehicle accessory to said alarm for triggering said alarm whenever the magnitude of the impedance from said second vehicle accessory to vehicle ground is less than a second predetermined threshold level; and means for coupling said alarm to a vehicle battery for triggering said alarm whenever said vehicle battery is electrically disconnected from said alarm.

Claim 3

A vehicle alarm system according to claim 1 further comprising: means for maintaining said alarm in an alarm condition for a predetermined minimum time interval after it has been triggered.

Claim 4

A vehicle alarm according to either of claims 1 or 2 further including a trembler switch for triggering said alarm whenever said vehicle is moved.

Claim 7

A method according to claim 4 further including the steps of: monitoring the voltage of a vehicle battery; and triggering an alarm whenever the vehicle battery is electrically disconnected from the vehicle.

Claim 8

A vehicle alarm system comprising: a switching circuit for activating an alarm relay having first, second and third control inputs and an output; an alarm relay having a control input and a first switch output, said control input coupled to said switching circuit output and said first switch output for coupling to an alarm; and a biased diode bridge coupled to said first control input of said switching circuit and for coupling to a vehicle accessory normally coupled to vehicle ground; said second control input of said switching circuit for coupling to a vehicle accessory that is grounded only when the vehicle is operating; said third control input for coupling to the vehicle's battery; said switching circuit biased such that it will be triggered and in turn trigger said alarm relay whenever the impedance between said biased diode bridge, through a vehicle accessory to vehicle ground is greater than a first predetermined threshold level, said switching circuit also biased to switch and trigger said alarm whenever the impedance between said second control input and vehicle ground drops below a second predetermined threshold level, said switching circuit also biased to be triggered whenever said third control input is disconnected from the vehicle battery.

Claim 9

A vehicle alarm system comprising: a switching circuit for activating an alarm relay having first, second and third control inputs and an output; an alarm relay having a control input and a first switch output, said control input coupled to said switching circuit output and said first switch output for coupling to an alarm; and a biased diode bridge coupled to said first control input of said switching circuit and for coupling to a vehicle accessory normally coupled to vehicle ground; said second control input of said switching circuit for coupling to a vehicle accessory that is grounded only when the vehicle is operating; said third control input for coupling to the vehicle's battery; said switching circuit biased such that it will be triggered and in turn trigger said alarm relay whenever the impedance between said biased diode bridge, through a vehicle accessory to vehicle ground is greater than a first predetermined threshold level, said switching circuit also biased to switch and trigger said alarm whenever the impedance between said second control input and vehicle ground drops below a second predetermined threshold level, said switching circuit also biased to be triggered whenever said third control input is disconnected from the vehicle battery.

Claim 10

A vehicle alarm system according to claim 6 further comprising: a second switch output of said alarm relay; and a timing circuit coupled by said second switch output of said alarm relay between said first control input and said output of said switching circuit for latching said relay for a predetermined time interval thereby establishing a minimum alarm time after said switching circuit has been triggered.

Claim 11

A vehicle alarm according to either of claims 6 or 7 further including a trembler switch for triggering said alarm relay whenever said vehicle is moved.

Claim 12

A vehicle alarm according to either of claims 6 or 7 wherein said switching circuit comprises: a first transistor biased to be conducting when not triggered by one of said first, second or third control inputs; and a second transistor biased to be nonconducting and having its base coupled to the collector of said first transistor, the output of said switching circuit taken as the collector of said second transistor, said first control input coupled to the base of said first transistor, said second control input diode coupled to the base of said first transistor, diode coupled to the base of said second transistor, and diode/resistor coupled to the emitter of said second transistor, whereby triggering of said switching circuit through any of said control inputs causes said first and second transistors to change state.