FM "Bug" Transmitter Electronic Kit from DIY Electronics
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.