Keyloggers
A keylogger is a software or hardware device that logs or records keystrokes in real time. They are used to troubleshoot technical problems with computers and networks. They could also be used to monitor the network and computer usage of people without their direct knowledge. So, this can also be misused on public computers to steal passwords or credit card information.
Hardware keyloggers
Hardware-based keyloggers can monitor victims' activities without any software being installed. They can be easily detected since, is a physical device that may be connected somewhere between the computer keyboard and the USB/PS2 port. There are more advanced hardware keyloggers that are not externally visible and are not dependent on any software. So, they cannot be detected by any software. But, a hardware keylogger requires physical access to the victim.
In the case of wireless keyboards, it is possible to intercept the signals sent from the keyboard to its receiver with a wireless sniffer.
