Hardware keylogger is a tiny module that plugs into your keyboard and captures all the keystrokes from your keyboard to its internal memory chip.
It resembles a standard keyboard (PS/2) connector cable but is equipped with a computer chip and a flash memory chip to capture and store the keystrokes instantly when they are typed.
It resembles a standard keyboard (PS/2) connector cable but is equipped with a computer chip and a flash memory chip to capture and store the keystrokes instantly when they are typed.
All you have to do is plug it in between your keyboard cable and your computer and it instantly starts recording the keystrokes. 
It works on any PC and is completely software free due to which it cannot be detected or disabled by any other software on your PC.
Besides using these keyloggers on a positive note to detect and prevent unauthorized use of company PC’s, they are also being used on public computers such as those at internet cafes, exhibitions etc., to steal your private data.
So, next time when you are accessing internet from public places check the back pannel connection of the keyboard (PS/2) connector cable plugged to computer to make sure it is free from any data feeders or keyloggers attached to it.