The very first store that I owned, way back in the day was an Optonica dealer. The Optonica RP-7100 had an extra sensor arm that rode along with the tonearm that detected the tracks. It actually sounded decent and worked pretty well.
http://www.mtk-physio.de/Info-Box/Optonica/Optonica_7100/Optonica_RP-7100/optonica_rp-7100.html
http://www.mtk-physio.de/Info-Box/Optonica/Optonica_7100/Optonica_RP-7100/optonica_rp-7100.html