Transmitter
One of the simplest kinds of hidden voice recorders is a transmitter bug. A small microphone is hooked up to a radio transmitter. When someone speaks nearby, the sound is immediately converted to a radio signal. The whole thing is usually powered by a battery. Usually, there is a listening station nearby where the signal is turned back into sound and recorded.
Cellphone
You may not know it, but you may be carrying a sophisticated transmitter bug on you right now. Some modern cell phones can be activated by law enforcement officials without the knowledge of the user. When they are activated, the microphone acts like a bug, picking up all nearby sounds and sending them to a listening station. This sort of bug is much more sophisticated than classic transmitter bugs. It can broadcast over a much larger distance (anywhere where there is cellphone reception) and is undetectable.
Miniature Recorder
Many hidden voice recorders are simply digital recorders disguised to look like something else. A pen recorder, for example, would look exactly like a pen and even be able to write. The spy would place it near to his target and turn it on with a hidden button. A small microphone would then record the conversation digitally on a microchip. When the spy was done, he could download the memory into a computer and recharge the pen's batteries.
For Best Results
Although all of the above-mentioned security devices work, they all have a flaw. If the microphone is out of position, it will not get the info you want. Miniature microphones often have poor quality, and only pick up sound at certain angles or beyond a certain range. The best way to bug a room is with a more low-tech solution: high-quality, conventional microphones which have been carefully hidden. Microphones can be built into the wall, hidden inside books, or even installed in appliances. By carefully preparing a room ahead of time, a spy can be sure that every corner is covered by the recording equipment.
Tags: hidden voice, hidden voice recorders, listening station, small microphone, voice recorders