JSoundspy records sounds from the main input line (usually, mic), and creates some 15s OGG files when the sound reaches a threshold (in dB). It can run during days.
JSoundspy needs Java 1.6 or more (and, fyi, use libvorbis/libogg from the Xiph.org Foundation).
JSoundspy is freeware.
(c) Askywhale 2012