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Movement in bed-placed pressure arrays often interferes with measurements. A method for automatically determining movement onset times from a bed-based pressure sensor array is proposed. By using control levels based on a moving average and the moving variance, the method can adapt to changing positions and postures of the bed occupant. A simulation was performed on a generated 24-hour pressure signal. The proposed algorithm accurately identified 97.4% of the simulated onset times. Experimental data from two subjects sleeping on the pad at night show similar results to the simulation. Using movement times, we may identify sleep restlessness as well as posture and position changes