Audio Interface Tamper Detection via Inaudible State Signal Multiplexing
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Solution Overview
Problem
Audio interfaces in alarm systems are susceptible to unauthorized modification or disconnection, and existing methods to deter tampering are costly and cumbersome.
Innovation Solution
An alarm system with an audio interface that includes a microphone, a state sensor, a signal generator for creating an inaudible state signal, and a combiner to multiplex the audio and state signals, allowing for tamper detection without interfering with audio reproduction, and using a single conductor to carry both signals to the control panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the audio interface is encased to deter tampering, then security is improved, but cost and device complexity increase
Solution Approach 1:
The patent extracts the tamper detection function from the physical encasing structure and implements it through a separate state sensor and signal generator. This allows tamper detection without requiring complex encasing mechanisms, resolving the contradiction between security improvement and device complexity reduction.
Solution Approach 2:
The patent introduces an intermediary state sensor and signal generator that mediates between the audio interface components and the control panel. This intermediary system enables tamper detection through electrical signals rather than physical encasing, reducing device complexity while maintaining security.
2Reliability
If multiple conductors are used to carry audio and state signals separately, then signal integrity is improved, but the number of physical interconnections increases
Solution Approach 1:
The patent merges the audio signal and state signal into a single conductor by using a combiner that combines both signals electrically. This allows both signals to be transmitted through one physical interconnection, reducing the number of conductors while maintaining signal integrity through proper signal separation at the control panel.
Solution Approach 2:
The single conductor serves multiple functions by carrying both the audio signal and the state signal simultaneously. This multi-functional use of the conductor reduces the overall number of physical interconnections required in the system while maintaining reliable signal transmission for both purposes.
3Measurement precision
If the state signal is transmitted at high frequency for clear detection, then detection precision is improved, but audio reproduction quality deteriorates
Solution Approach 1:
The patent applies local quality by treating the state signal and audio signal differently in terms of frequency characteristics. The state signal uses a specific frequency range that is distinct from the audio range, allowing clear detection while preventing interference with audio reproduction. The combiner and control panel are designed to properly separate and process each signal type according to its specific requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables effective tamper detection and reduction in physical interconnections, enhancing security and cost-effectiveness by allowing for real-time monitoring and alerting of tampering attempts without disrupting audio communication.
Implementation Method 1
a state sensor for sensing a state at the audio interface
Implementation Method 2
an audio interface comprising: a microphone
Implementation Method 3
a combiner for forming a combined signal from an electrical signal corresponding to audio sensed at the microphone, and the state signal
Data Source
AI summary
An alarm system comprises: an audio interface comprising: a microphone; a state sensor for sensing a state at the audio interface; a signal generator for generating an inaudible state signal indicative of the state; a multiplexer for combining an audio signal from the microphone and the state signal; a control panel for monitoring sensed conditions at the audio interface; a conductor interconnecting the audio interface to the control panel carrying audio signal and the state signal as combined from the audio interface to the control panel.