Spy equipment - Hardware key logger

Hardware Key loggers can be used for Keystroke logging. They plug in between a computer keyboard and a computer and log all keyboard activity on an internal memory.
Hardware Key loggers come in two versions:

-As small devices about the size of a AA battery that are plugged in-line with your keyboard.
-As a normal looking keyboard with an internal key logger, or Trojan Keyboard.

They are designed to work with PS/2 keyboards, and more recently with USB keyboards.
Hardware key loggers have an advantage over software key loggers as they begin logging from the moment a computer is turned on (and are therefore able to collect a BIOS password for instance), and do not require software installation (unlike software solutions).
How do they work?
All hardware key loggers have to have the following:
A microcontroller - this interprets the datastream between the keyboard and computer, processes it, and passes it to the non-volatile memory
A non-volatile memory - this stores the recorded data, even when power is lost
On the whole the recorded data is retrieved by typing a special password into a computer text editor. As the hardware keylogger is plugged in-between the keyboard and computer, it detects the password has been typed and then starts presenting the computer with "typed" data to produce a menu.
These devices are spy equipment generally used by companies to monitor and spy employees, private investigators looking for evidence, or really serious identity thieves who want to keep track of what you do on your computer.
Hardware keyloggers are generally advertised as being better than software keyloggers because they are undetectable. This is true for the uneducated; however after reading this page you will be able to spot a hardware keylogger with ease!