An apparatus is provided for detecting mating of a cap with a fluid delivery device having a housing, a receptacle, and a sensor. The housing is configured to carry an insulin delivery device having a reservoir of the fluid. The receptacle is provided by the housing having a coupling with a locking recess configured to receive a cap with a sprung locking arm. The pressure sensor is carried by the receptacle proximate the coupling and configured to detect engagement force of the sprung locking arm with the receptacle when mated with the housing. A method is also provided.