Methods and devices for monitoring the position of a subject are disclosed. One such method includes sensing pressure waves generated by the subject moving on a divided bladder comprising interleaved portions, generating signals indicative of the pressure waves for each of the interleaved portions, and sending the signals to a processor. The method further includes determining the position of the subject based on the difference between the signals from each of the interleaved portions and generating a pattern for the subject. The pattern includes the presence and/or position of the subject over time. The method further includes predicting an action such as an exit of the subject from the divided bladder based on comparing a current pattern for the subject to previous patterns for the subject.