Conn ST-11 Strobotuner

The Conn ST-11 Strobotuner is a guitar tuning device. It was used by Andy Summers whilst touring & recording with The Police (at least) during the early 1980s. And also Stewart Copeland, who had one around at his home studio (the "Worried Rabbit" as it would be known).

Source

 * L'Historia Bandido (1981) by Phil Sutcliffe and Hugh Fielder - photos included
 * Klark Kent "Away From Home" video & various home studio photos