A surgical knife safety device having a handle, a blade connected to the handle, and a guard carried by the handle for sliding movement between a retracted position in which the blade is exposed for use, and an extended position for covering the sharp cutting edge of the blade. A spring, such as leaf spring or a cantilever beam, and a pair of detents or slots are provided to fix the guard in the extended or retracted position and to provide resistance during movement between the two positions.