Yes, this is a device that can be added to a striker-fired Glock pistol to make it safer, but it's not a safety.
The Glock Striker Control Device (SCD) from the Tau Development Group—commonly called The Gadget—replaces the back plate on a Glock slide (where the hammer would be on a hammer-fired pistol) that makes the gun safer during the operation where an accidental discharge is most likely to occur: when it's being holstered.
Let’s be clear, the Gadget isn’t an actual safety. First, it’s a visual indicator. When any rearward pressure is applied to the pistol’s trigger, you can see the gadget begin to rise from it’s normal flat position.
When a striker fired pistol with no manual safety is holstered, and something manages to put pressure on the trigger, there’s nothing stopping it from firing. How could this happen? With popular carry styles like IWB and appendix-position carr, a piece of clothing or the edge of a belt could conceivably get stuck in a holster unseen to the shooter. Even at the range, a piece of brass could land in the holster. It’s not common, but it happens.
The Gadget allows shooters to train themselves to keep the device depressed with the thumb while holstering the gun. This allows the user to feel if the Gadget tries to rise, meaning the trigger is being pressed and something isn’t right. Additionally, the thumb pressure on the gadget will prevent the trigger from firing the gun, even if the pistol is pushed farther into the holster before it’s apparent something’s amiss.
It mirrors a training method for holstering double-action, hammer-fired pistols and revolvers, in which the user keeps pressure on the de-cocked hammer, preventing the trigger from accidentally being engaged. The Gadget allows you to essentially do the same thing.
The whole point of having a striker-fired pistol in a Glock-like configuration is to remove most external controls, making for a smoother snag-free draw. Fewer controls also means the gun is simpler, easier, and faster to use under stress. With proper training, this kind of handgun is perfectly safe, but there’s no way to train for holster obstructions, short of tactile or visual inspection of the holster before inserting the gun each time—which is hardly practical.
The Gadget allows Glock users to prevent putting an accidentally discharged round through their holsters, or worse, through themselves, while being completely passive during normal operation, not interfering or adding an extra step in any way.
The SCD fits all Glock models except the G42 and G43, though a variant for those models is forthcoming, according to the company’s website.
You can buy an SCD there for $79. Though it isn’t stated, there does not appear to be any gunsmithing required for installation.