Slotted proximity sensors consist of a two coil system sensing across the slot opening. If a piece of metal is inserted into the slot sensor, the inductive coupling between coils will be reduced based on the depth of the target metal. Once this coupling falls below its critical value the proximity switch will be activated.

Due to the nature of the sensor design, this type of proximity switch is less affected by metal characteristics as well as being less sensitive to target position changes in the direction of the core axis.