The product below may be in a room in an edge and transmit voice be done in the other edge of the room ? The Mic how many distance is capable to listen ?
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http://www.hobbyengineering.com/H1481.html
FM "Bug" Transmitter Electronic Kit

This is a fun kit to practice soldering and learn a little bit about electronics. This is the most powerful 'bug' available for its size, 3V supply and number of components. It is guaranteed to transmit over 100 meters within buildings and up to 500 meters in the open. Easily tunable in the FM band. Greater range can be achieved with higher voltage and/or a better aerial. An excellent introduction to the theory of 'simple' 2 stage transmitters is available for download.

Data Sheet http://info.hobbyengineering.com/specs/DIY-k7.pdf

Mfr: KITSRUS

Mfr. Part No.: K007

 

I could not find any information on the website concerning the sensitivity of the microphone.

At $10 US the cost is low enough to purchase it and see how sensitive it is for yourself.

I would imagine that normal conversation levels could be picked up reliably from 5 feet away. However, a whisper would probably not be picked up at all from that distance.

hgmjr

 

As with any mic system, ambiant noise will probably make it impossible to hear a gnat sneeze.