Update. I looked at Digikey and found http://www.knowles.com/download/file?p=SPU0410LR5H.pdf is the only one they have currently (Feb 2015) that displays a frequency response above 10Khz. This unit goes from 100 Hz to 80 Khz with a 10 dB peak at 25Khz and an -8 dB broad dip at 60 KHz. That is not fl...

I too have been interested in bat call detection. Bertrik's pages and info are very good. 10 years ago or so, when I got interested in this, Knowles had invented the Sisonic mircophone. It was a freefloating silicon microphone. Very small, like a matchhead. Invented specifically for the cell phone m...