To enable the Accessible Login feature to use alternative pointing devices and switch devices such as sip-and-puff switches, wheelchair-mounted switches or trackballs, you might need to modify your X server system configuration to recognize these devices. You can use most devices that emulate mouse buttons with the Accessible Login feature and On-Screen Keyboard, including USB single switches and mouse-like pointing devices.
You should not configure an alternative input device to control the primary on-screen pointer. This might result in undesirable behavior or cause situations from which the user of the alternate input device cannot recover without using the primary keyboard or mouse. To prevent this problem, remove any occurrences of the attributes SendCore or AlwaysCore from any of the InputDevice lines in the X Server configuration file.