Method of monitoring a vehicle interior

DETAILED DESCRIPTION We claim: 1.
A method of monitoring an interior of an automotive vehicle against an incursion, said method comprising the steps of: (a) detecting sound waves in said interior; (b) converting detected sound waves into electrical measurement signals representing the detected sound waves; (c) amplifying said electrical measurement signals and supplying amplified electrical measurement signals to a computer; (d) storing in said computer sample signals representing incursion conditions; (e) automatically in said computer comparing said amplified electrical signals with the stored sample signals in accordance with a test function constituting least one of an identity test function and a similarity test function; and (f) automatically with said computer triggering an alarm upon determination of an incursion determined by said test function by comparison of said amplified electrical signals with at least one of the stored sample signals, sound waves detected in said interior being generated by superimposition of sound waves on sound waves reflected within said interior from a sound wave emitter generating primary acoustic pulses in the vehicle interior, said sample signals stored in said computer representing sound waves produced by a primary sound wave source and reflected in a vehicle interior and other sound waves superimposed thereon.
2.
The method defined in claim 1 wherein said electrical measurement signals are transformed by a rectifier and a filter into an envelope-measurement signal which is compared in said computer with envelope-sample signals representing incursion conditions.
3.
The method defined in claim 1 wherein the test function is carried out with sample signals representing sound waves generated upon breakage of a vehicle window.
4.
The method defined in claim 1 wherein a plurality of sound wave detectors are provided for the interior and produce respective electrical measurement signals which are fed by a multiplexer to the computer.
5.
The method defined in claim 1 wherein the electrical measurement signal is subjected in said computer to spectral analysis and the spectrally-analyzed signal is compared in the computer by said test function with at least one spectral analysis sample signal stored in the computer