Abstract: A circuit for sensing keyboard input conditions, which includes a slot coupled to regulated signal lines, a supplementary circuit which generates a "Low" active signal in accordance with keyboard input activity after taking input signals from the slot, and a logic device or controller which performs a power-saving function by sensing input conditions from said slot with an interrupt request line or the supplementary circuit. The so-modified system can overcome the limits of a PC, in which the power-saving function can be performed only in the motherboard, by adding the power saving function to the system which has no logic device in the motherboard and also by sensing keyboard input conditions in a logic device included in an option card. This circuit can generate the appropriate signal by monitoring the regulated slot signals and has the same power-saving function that is performed in the motherboard itself when there is no keyboard inputting for a predetermined time.