Switch Click USB

Description
A switch and interface in one. Simply plug this 2.5-in/6.4-cm diameter
switch into any USB port on your computer and press to simulate a left
mouse click, while maintaining full access to your keyboard and mouse.
Switch
Click USB features an external switch jack to accommodate the switch of
your choice. In addition, simple adjustments allow it to send Left
Click, Right Click, Space, Enter, Tab, and Arrow keys: Up, Down, Left
and Right. Now you can have full access to two-switch scanning, any way
you like. (Requires purchase of a second Switch Click USB).
Switch Click USB