2012 is international year of the bat: www.yearofthebat.org. Get listening to these amazing creatures with the bat detector.
A workshop to build a bat detector will run on Tuesday 10th April 2012. Starting at 7pm. This workshop will cost £20 and include all components, professional circuit board, instruction and guidance to build your own. Learn to solder: no experience required.
Details of the design are here on the wiki.