There are some devices that can be used as both input and output devices. These are:
1. Touch screen monitor: A touch screen monitor can be used as both an input and output device. It can display information to the user and also accept input from them through touch.
2. Digitizer: A digitizer is another device that can act as both an input and output device. It is used to convert analog signals, such as handwriting or sketches, into digital form. It can also display the digital output on a screen.
In contrast, devices like a scanner and speaker are typically designed to perform just one function. A scanner is primarily an input device that converts physical documents into digital images, while a speaker is an output device that produces sound.
To summarize, touch screen monitors and digitizers can be used as both input and output devices, while scanners and speakers are typically limited to a single function.