Resources Contact Us Home
Intrusion detection method and apparatus

Image Number 2 for United States Patent #4229811.

An improved method and apparatus for carrying the method are disclosed which provide for selection by the user of a surface used as a reference in the detection of an intrusion. This is achieved by periodically projecting pulses of acoustical energy from a source towards a reference surface and detecting the reflection of such pulses of acoustical energy at a receiver and providing a first indication or signal representative of the reflected pulses. A second indication or signal is generated which is adjustable and representative of the time elapsed between the projection of a pulse of acoustical energy from the source and the reception at the receiver of the pulse of acoustical energy when reflected from the selected reference surface. The variations between the first and second indications are detected and compared and an alarm is generated when a variation is detected in the indications. In the embodiment disclosed, the absence of variations between the first and second indications is measured by the coincidence of the first and second indications.

  Recently Added Patents
Display apparatus and control method thereof
Mobile terminal device capable of more effectively utilizing operation portions, conductive portion, operation detecting unit, power supply unit, and signal processing unit
Liquid crystal shutter glasses
Evaluation compiler method
Mobile terminal and controlling method thereof
Optical packet signal transmission device and WDM optical communication network
Method and apparatus for transmitting and receiving a signal in a communication system
  Randomly Featured Patents
Fluidizable zinc titanate materials with high chemical reactivity and attrition resistance
Senna dosage form
Whole transciptome sequencing
Quick connect connector with tolerance accommodation
High-strength and temperature-change resistant ceramic formed body, especially of mullite, its production and use
Tamping tool
DC-DC Converter
Video communication system and phase or frequency modulator included therein
3,3-(disubstituted) cyclohexan-1-ylidine acetate dimers and related compounds