In-bed motion detection is an important techniquethat can enable an array of applications, among which aresleep monitoring and abnormal movement detection. In thispaper, we present a low-cost, low-overhead, and highly robustsystem for in-bed movement detection and classification thatuses low-end load cells. By observing the forces sensed by theload cells, placed under each bed leg, we can detect manydifferent types of movements, and further classify them as bigor small depending on magnitude of the force changes on theload cells. We have designed three different features, whichwe refer to as Log-Peak, Energy-Peak, ZeroX-Valley, that caneffectively extract body movement signals from load cell datathat are collected through wireless links in an energy-efficientmanner. After establishing the feature values, we employ a simplethreshold-based algorithm to detect and classify movements. Wehave conducted thorough evaluation, that involves collecting datafrom 30 subjects who perform 27 pre-defined movements in anexperiment. By comparing our detection and classification resultsagainst the ground truth captured by a video camera, we showthe Log-Peak strategy can detect these 27 types of movementsat an error rate of 6.3% while classifying them to big or smallmovements at an error rate of 4.2%.