While many bicyclists use so-called "clipless" pedals for serious cycling, simple platform pedals are often better for quick, casual rides. Pocket Pedals are designed to bridge the gap between the two, temporarily converting clipless pedals into platforms.
First of all, yes, you're right – there are already flat plastic doohickeys that can be clicked into the engagement mechanism of third-party clipless pedals. As is the case with Pocket Pedals, these allow users to wear regular shoes (instead of cleat-equipped cycling shoes) when running errands, riding with family members, or otherwise doing things where convenience is more important than performance.
Icelandic cyclist Karl Birgir Björnsson had tried those click-in gadgets, but found that the foot platform was too small, they only covered one side of the pedal (causing that side to flip downwards when his foot wasn't on it), plus they were difficult to remove. This led him to team up with an engineer friend, and invent Pocket Pedals.
Made of a durable polymer, the devices fold flat when not in use, allowing them to be stuffed in a jersey pocket. Once needed, they're just folded open, then slipped over the user's SPD-style road or mountain bike clipless pedals. Grip studs on the exterior of both sides subsequently keep the soles of rider's shoes from sliding off, while the interior contours of the Pocket Pedals are claimed to keep them from accidentally coming off the clipless pedals while riding.
"We have tested them thoroughly and there is very little chance of them falling off," Björnsson tells us. "We faced that issue with previous versions but I have yet to manage to make this final version of the product fall off my pedals. With enough will and force, one could probably do it, but under any normal riding circumstances it doesn’t happen."
Pocket Pedals are currently on display at Eurobike 2019, and can be preordered for €39 (about US$43) via the link below. They're demonstrated in the following video, and should ship at the end of the month.
Source: Pocket Pedals