Bought this for my brother. Don't know what he wanted it for (hee hee!).
It is tiny & plugs in line with the keyboard connector on a PC (PS2 connector NOT USB), probably around the back of your PC where it is difficult to see it.
It logs every keystroke that is typed and has a big memory.
When he tried it on my PC, the pc made a bleeping noise (maybe my pc has some kind of system to detect bugging of this type?), but when he tried it on another PC it worked fine, with no sound, to give away its installation.
It has a password system which you set up, & it outputs all the keystrokes it has logged, when the password is entered on the keyboard, so if you are using it surreptitiously, in 'stealth' mode, you had better not make the password something obvious like 'password', otherwise, if the person you are bugging, types in 'password', it will spew all the keystrokes it has been logging, into the document they are working on! Oh and if you do make the password something completely random, you had better write the password down, cos if you forget it, it will be locked forever!