Ok. So to be candid, a $10 knife is likely a POS. Nevertheless, the concept is a notable one. And honestly, if you never plan on using it in a tactical (i.e. fighting) scenario, who cares.
Say hello to the Tac Force TF-530BK Tactical Brass Knuckle Knife. Unfortunately, the description on Amazon’s page is sparse to say the least. Nevertheless, it’s said to be made of steel and includes a teflon coated blade that measures just under 4-inches in length (3 5/8″ to be exact). If you look closely there is a small metal knob at the base, which can be used to break open a car window in an emergency, or worse puncture someone’s skull – I suggest sticking to windows. Although it’s not a switch blade, there is a spring that should lend an assist in opening, as well as a belt clip for keeping it at a hands reach.
You can buy the Tac Force TF-530BK Tactical Brass Knuckle Knife for $10 at Amazon.