Method and apparatus for detecting a hazard detector signal in the presence of interference

An apparatus for detecting a pattern warning signal from a hazard detector in the presence of a second pattern warning signal from a second hazard detector, comprising:

• a transducer for converting the pattern warning signal and the second pattern warning signal to a composite electronic signal, each of the first and second pattern warning signals comprising an on-time period followed by an off-time period;
• an analog-to-digital converter for converting the composite electronic signal into a digital signal;
• a memory for storing processor-executable instructions and one or more thresholds;
• a transmitter for transmitting an alarm signal;
• and
• a processor coupled to the analog-to-digital converter, the memory and the transmitter for executing the processor-executable instructions that causes the apparatus to:
• determine an on-time duration of the digital signal as a time that the digital signal exceeded a first voltage threshold stored in the memory;
• and
• transmit an alarm signal to a receiver when the pattern warning signal has been determined to be present, based on the on-time duration.