Seen in "Lemons" - episode 3 of Season 10 - this is a replica of the remote control for the rejuvenation shower. When the crew of the Red Dwarf are accidentally sent back in time by a malfunctioning rejuv shower, they have to track down lemons to make a battery to power the remote to send them back to their own time. The item used in the show for the remote control was a digital ultasonic distance measuring device.
