It has to be cheap (even disposable). It has to last days, even weeks. It has to be flexible - different audio for different 'target' animals.
Here is the first prototype of the TrapTalker. It is cheap, even disposable. It is flexible - load any sequence of calls, pauses, etc. onto the SD card and let it go. And its small.
Here is a solar option - to charge and extend the internal battery on the MP3 player. Only issue with this, eventually the amplified speaker (internal AAA batteries) will wear out and hamper the sound.
Several options - amplified sound vs. un-amplified (less expensive, less range). Both speakers can be used together... or individually. This combination will keep broadcasting even when the amplified speaker dies out.
Initial testing is just a zip-tie holding the TrapTalker inside the cheap plastic container and out-of-the-weather. We'll keep you posted as we do some field testing... maybe with a trail camera too ;-)
Here is a simple demo out in the back.