An apparatus and method for detecting a difference in width of a strip of material from a desired width of material. The apparatus may comprise a light source, a light detector, an alarm, a first fiber optic cable coupled with the light source, a second fiber optic cable coupled with the light detector, and a housing. The housing may comprise a material slot for passing the strip of material therethrough such that edges of the strip of material may at least partially intersect a plurality of light fields directed from the first fiber optic cable to the second fiber optic cable. The amount of light detected by the light detector is dependant on the amount of light blocked by the strip of material. If the amount of light received is outside of a range of tolerance from the desired width of material, the alarm may be actuated.