serial_sniffer -- Serial Sniffer allows you to sniff serial data
http://www.ibiblio.org/[..]inux/apps/serial_sniffer-0.5.tar.gz
serial_sniffer by Grahame M. Kelly (gmkelly zip.com.au) The Linux Serial Sniffer allows you to sniff serial data up to 460Kbs via a Comtrol RocketPort or to 115Kbs using the standard ttyS0 and ttyS1 ports. Sniffed output can be captured to disk or displayed directly on screen. A user filter is included to assist specific customisation. The Linux Serial Sniffer can selectively operate in either a "ghost mode" where there is no data flow time impediments, or via a "capture and forward mode", where the user can flexibily intercept and extend the data stream to suit from either direction.