The Stinger Pengun is a single shot pistol, designed to look like a pen until it is ready to be fired. Because, however, the Pengun has to be reconfigured from its baseline pen shape to a more traditional gun shape before being fired, the ATF does not classify it as a "gadget gun," and hence anyone seeking to buy a Pengun is not required to go through the background checks required of anyone who wishes to purchase a gadget gun.
The Pengun is produced by the Stinger Manufacturing Corp. of Saulte Sainte Marie, Michigan, for about the past two years, and was originally designed by the R.J. Braverman Company.
Because of post-9/11 fears about airport security, there are questions of whether the ATF should change the Pengun's National Firearms Act classification from "Title I handgun" to "Any Other Weapon," at which point additional background checks for purchasers would come into play. However, at the time of this writing there has not been a documented case of someone being caught trying to bring a Pengun onto a plane.