1. An mobile device to monitor human activity using multiple sensors comprising: a plurality of sensors; a dedicated processing unit receiving data from the plurality of sensors, the dedicated processing unit to process sensor data, the dedicated processing unit further comprising a calculating logic to compare a first estimation of a user activity statistic based on data from a first sensor with a second estimation of a user activity statistic based on data from a second sensor, and calculating the user activity statistic based on the first estimation and the second estimation, wherein the calculated user activity statistic is a result of a weighted combination of the first estimation and the second estimation; and a central processing unit to perform functions in the mobile device.